@JonasResende, there are sourced on Maria Anna Karoline from the German Wikipedia that explains why she never married. She caught rickets at age three and developed a slight spinal curvature as well as apparently losing her sight in the left eye (the translation isn't great but calls it a star disease in the eye and later mentions an eyepatch of green taffeta. Plus she did have a religious calling; after a failed love affair with her uncle Prince Konstantin Sobieski, she entered the Order of St. Clara in 1719.
As for Josef remarrying, the is his STD (supposedly Syphilis). We know he passed it to Wilhelmina in 1704 and that it supposedly made her barren. Now I have contested this several times over the years (Wilhelmina had a pregnancy a year from 1699 to 1701, yet none in 1702 and 1703; the STD wasn't passed to her until 1704. It's just as possible that complications form the 1701 pregnancy rendered her infertile and the Court simply blamed the STD instead) but the possibility is there that Josef wouldn't father a son with a second wife.
And if we go with a son of Carlos III succeeding Josef, it becomes the question of which? Does Josef demand the eldest or would be be content with a second son?
Thanks for the info on Maria Anna Karolina, I did not know that. I always just assumed it was perhaps due to the fact that her father was seen as a fair-weather friend by both the French and the Austrians that she never married. Didn't know about the health issues.
As to first or second son, Joe might decide to pull a repeat of Karl V. He can't take his oldest nephew, since he has no assurances that there will be other boys - he and Karl VI only had one apiece OTL, his dad only had five (of which only three made it past their final year) - and the Spanish might take issue with the child that they see as Spanish being sent to Vienna. IMO, once the second boy is born, Joe will probably order him to be brought to Vienna.
Yes, it seems that for the Brits an issue of the Stuarts succession/restoration was close to the top of the list (and perhaps the right to sell the slaves to the Spanish colonies). So if Louis did not declare his support of the Stuart cause (rather idiotic move) and did not insist on his candidate not being excluded from the French succession (again, quite idiotic at that time: there were numerous French princes still alive by 1700 and, strictly speaking, with the legitimization of his bastards, there was more than one candidate even by the end of the war) the whole thing could be avoided and replaced with a peaceful partition of the Spanish possessions in Europe. The Austrian Hapsburgs hardly could sustain a prolonged war with France strictly on their own even with a trump card like Prince Eugene (who was seemingly well matched by Villars). At best they would be able to gain on one theater (Italy) with the French having a more or less free hand elsewhere.
Yeah, I'm not sure what Louis was hoping for. Antonia Fraser writes in her bio of him that it was simply not in Louis' nature to turn away this for the aggrandizement of his dynasty. All well and good then. But the Stuarts were not Bourbons. They were clients of the Sun King much like numerous princes etrangers were. He didn't go trumpeting the claims of the de la Trémoïlles or the Guises to the Neapolitan throne, so why he decided the Stuarts were a good bet, I'm not sure. Britain will get involved as long as France wants the Low Countries - she was like a proverbial dog in the manger about that (nobody but France wanted it, and nobody but England wanted the French to have it) - and will probably not want it to end up in th ehands of a French proxy like Max II of Bavaria or the duke of Savoy. If France and England can come to an agreement about leaving those alone, England and the Dutch won't get involved - hopefully William III's personal vendetta against Louis can be left out of the negotiations.