To solve question of MQOS French marriage-if Mary Tudor takes the throne in 1548 instead (so there is short period of Eddie's rule) when Mary of Scots is already in France then her marriage to Dauphin is certain. But death of Henry II in freak accident is unlikely to happen ITTL-although last Valois were rather not long living so we can assume that Henry II still dies before his son and MQOS is still Queen of France at least for few months. Then widowed Mary returns to Scotland and few years later marries another king...
Wasn't Francis sickly? If his father doesn't die as OTL, Francis will still die around the end of 1560 and Mary, as the anointed sovereign of Scotland, is now 18 and NEEDS to go to Scotland or lose her kingdom there (if she's not with her husband, she needs to be where her kingdom is).