PC: 'For Want of a Broker' - Bismarck's death in 1877 leads to two major European wars in 1878

Here is the general outline of an idea I had for a timeline, and I wanted to know what you thought of its plausibility:

Bismarck catches a fatal case of pneumonia over-celebrating indoors and outdoors with schnapps, gluwein, and maybe eggnog in Christimas 1877, he is dead before January 1878 is out, and his successor as Chancellor has a difficult time filling his boots

March 15th, 1878 - Russia presents its draft Treaty of San Stefano, with Turkey, settling the Russo-Ottoman War, to the world, and most of the states of Europe who aren't Russia or Russia's Balkan allies find its terms, the creation of a 'Big Bulgaria' astride the Balkans from the Black Sea to the Mediterranean and nearly the Adriatic, the enlargement of Romania, Serbia, and Montenegro, way over the line and contrary to the promises of a 'reasonable' settlement Russia pledged it would impose on the Turkish Balkans before and during the war. Austria-Hungary in particular feels betrayed and duped. Britain, as usual, has the vapours about Russian aggrandizement of almost any kind and amount, directly or by perceived proxy (Bulgaria).

The new German Chancellor, nor the German Emperor, are willing or able to put themselves forward as an honest broker and mediator between Russia and Austria-Hungary and Britain. They fear alienating either of their Dreikaiserbund allies, St. Petersburg or Vienna, and lack the confidence they can steer matters to an agreement any better than the parties themselves. They lack the skill and command to persuade all parties to assemble in Berlin for great power talks to come to a binding settlement taking into account everyone's positions. - IE, there is no 1878 Congress of Berlin to resolve/mediate the 'Eastern Question'

The drift in German policy allows the most concerned powers, Britain, Austria-Hungary, Russia, and the Ottoman Empire, to drift along on with bargaining which is more like posturing and a collision course.

With London and Vienna encouraging each other with promises of support against Russia, London offering financial, naval and limited military, the Austro-Hungarians offering military contributions, both states in turn issue an ultimatum to Russia to greatly pare back its demands from the San Stefano borders, to something like the OTL Congress of Berlin borders, or something even less generous to Russia and its clients and more generous to the Ottomans. When Russia refuses the ultimatum, they both declare war on Russia. Austria-Hungary mobilizes its Army in Transylvania and Galicia, and Britain sends its fleet to the Aegean, along with some available troops.

With the British and Austro-Hungarians committed to a war on Russia by May-June 1878, with open war aims or rolling back Russian and Russian proxy gains, Romania, and probably Serbia, and possibly Montenegro, and Bulgaria (unrecognized), declare for the Russian side. The Ottomans, being promised a degree of restoration, and British financial support, naturally declare for the Austro-British support. The British and Austrians are please to have the Ottomans open the Turkish straits for British ships, while the Russians are livid. The Greeks, while anti-Ottoman in sentiment, sit tight and inert, recognizing the complete vulnerability of their coastline to British seapower.

Essentially spring-summer 1878 has brought us, after a brief intermezzo from the Russo-Ottoman ceasefire and period of diplomacy, into 'Crimean War II', with the same major players as in Crimean War I. The biggest change is that in this sequel, Austria-Hungary has taken over the role of France as Britain's European continental land-hybrid-sea power ally.

Another difference is that Italy, the larger successor to Piedmont-Savoy, is not interested in joining the British-led posse, because it has nothing material to gain from Russia, they prefer Austrian territories if anything, and Vienna howled with mirth when the Italians suggested lending support to win Austria land in the east in compensation for Austrian land to Italy right now. At the same time, much as poaching land from either the Austrians or Ottomans might be a temptation for Rome, it is unacceptably risky with both empires allied with Britain for the moment.
France is also temporizing and avoiding intervention for now. All things being equal, it would prefer a quiet east. But it is in no rush to pick sides in a war between Britain and Russia. It is still rebuilding from the Franco-Prussian war. It's first, second, and third priorities are defense of the eastern border with the new German Empire, and being an enemy of either London or St. Petersburg is far from optimal - Paris' ideal outcome would be it aligning with *both* St. Petersburg and London, but the current situation points 180 degrees away from that happening.
So Crimean War II is happening, and should go on at least 8 to 10 months, if not more. Russia has depth and people, but financial and equipment weaknesses. The other guys should have better tech but would have their own bungles.

In the midst of these powers busying themselves, Moltke and the rest of the Prussian General Staff come out strongly advocating that this is the time and the season to settle accounts with France, which has been unpleasantly surprising Germany with the speed of its recovery from the Franco-Prussian war, and the build-up of its forces and fortresses. Indeed France demonstrated its diplomatic cleverness and determination to outmaneuver and embarass Germany by exploiting the War in Sight crisis of 1875 by making Germany look like the aggressor, and maneuvering the Russians and British to look like they were interceding to offer protection for France. There were no further reports of any real French alliance-building since then, but the French agenda was bared and as clear as day, as clear as their desire for revenge. Moltke presents to the Kaiser and Chancellor a plan to broadly attack France across the common Franco-German border by late summer (August-September) to crush its armies and fortresses, while every other power of major military importance in Europe is engaged in war with each other. Indeed, Germany will invite the one uncommitted power, Italy, to participate on its side, once the attack on France is underway.

The Kaiser is impressed with the meticulous planning and confidence, but asks, "What are we seeking to win from France exactly? What do they have left we want? Even when we prevail, how do I know you will not be presenting with the same arguments and plan again, eight years from now? "

To this, Moltke replies, "I consider it a duty to inform you that war with France now would be less disadvantageous than at some other time of France's choosing after she has made additional military and diplomatic preparations. As for what we must win, we must capture and destroy her fortress line before it is consolidated, crush her mass army, and the officer cadre that has been training to lead it before it is fully institutionalized as our own, extract additional indemnities to hobble her military development, and extend our defensive buffer in the Lothringen Reichsland forward to the Moselle river, eliminating the French salient that intrudes into Elsass-Lothingren, and extend forward to Longwy, to seal off France from Luxemburg and seize that region's iron deposits, at a bare minimum, and I suggest you consult with your other ministries and departments, and Stosch in the Navy, on any other territories required, continential or colonial, that may be required that I have not thought of. So you see your highness France still possesses assets dangerous to us in their hands and useful in ours. As for eight years from now, I am no prophet. Should I be so lucky cannot say definitely what will or will not be required in the decade ahead. On a hopeful note, I would only say that with our superior birthrate in Germany, consistent over decades, the French can ill afford the losses we can sustain. Pupils and recruits learn from consistent discipline. So can countries. The Swedes, Danes, Dutch, Spaniards, all learn not to play above their 'weight-classl eventually, and reduced their ambitions to the scope of their capabilities, regrettably the war of 1871 did do that for France, but perhaps only one more repetition will be needed."

So the Germans launch their invasion of France in say, early September, 1878, after working up a crisis atmosphere for the several weeks beforehand. The early campaigning of the Crimean War II is still going on, and not easily interruptible, so Britain, Russia, Austria, cannot easily stop everything and shift attention and forces to do anything relevant to the Franco-German conflict. If it looks like a replica of the Franco-Prussian War, they may not even be motivated to do so. The German forces, for example, are not invading Belgium or trying to annex lands on the English Channel or Atlantic coast. Are the Germans going to be able to win against the French in a year as in the Franco-Prussian War? Or will the French Republic's changeover to a conscription-based army have made the French a much tougher nut by 1878? Could there be a stalemate on the mutual frontier that makes violation of Belgian neutrality a tempting or necessary looking option to the German side, after the war starts? Could the French surprise me, smash the German advance, gain the initiative, and reclaim their lost provinces, pushing the Germans back?

Presuming a reasonable amount of German success falling at or above expected German success levels, would Rome entertain German offers of territories at French expense (Savoy, Nice, Corsica, possibly part of Algeria) in return for alliance and Italian joint prsecution with Germany of the war against France? This would require some boldness and willingness to accept costs on the part of the Italians, and certain patriots like Garibaldi would hate the idea, but the territorial reward would be obvious. And the Rome issue had been settled eight years earlier, so it no longer 'stood ahead in line' of other gains at France's expense. For a Germany that is going to war with France anyway, the benefits of an Italy partaking in combat on its side, and in territorial gains in the peace are also obvious for both warfighting and postwar in terms of having a partner to share French enmity with.
Could and would these two war, Crimean War II, and Franco-Prussian War II (+Italy) stay as separate, parallel wars going on a couple years? Or would they be likely to commingle into a single war of two great European coalitions. If the latter happened, what would likely cause it?