Good questions! Queen Mary the Queen Mother died of injuries on October 3, 1940, five days after King George VI died in the same Blitz raid.
Hmm. So, Philip and Elizabeth were already acquainted and "talking" by 1939, with the future Queen expressing an interest (though only 13, with him being 18). By the time of the death of King George VI, Philip is serving with the RN in the Indian Ocean, though with the crisis and the invasion, I'd imagine he's transferred back to Britain. Elizabeth II and her court are evacuated just before her 16th birthday in 1942. Philip would be 21 and, if he's alive, on a ship. Now, a lot of people had been against the match to begin with. It's conceivable that, even if Philip had survived to this point, the courtiers would have tried to secure another match for the queen. I never established who she married, just that she, along with her husband, son, and two daughters, perished in WWIII.
As far as Margaret, I honestly saw her as more of an anti-Elizabeth. Yes, she disliked the Nazis for upending her life, but after the armistice, she asked to return to London instead of being "stuck in provincial Canada" in the late 1940s/early 1950s, a request that the Queen and the court denied. She grows up disliking life in Canada, and although shocked and horrified at the sudden and abrupt death of her sister, she's happy to be back in the UK and gladly accepts her role as heir and then as Queen in her own right in 1975 when Edward VIII dies. Now, for the twenty-six years she is on the thrown she is basically a puppet of the BUF and the Nazis, but an active puppet.
Margret was married to the fictitious "Prince Harold" and their eldest child is the future King Henry IX, who is born in the chaos of 1971 and is still in his prime during the 2012 SS Coup and other events of the Book.
Hadn't thought about Queen Wallis in a sort of "Queen Mother" role. But you're right to bring her up. OTL she lived until 1986. Accounting for the added stress of actually being on the thrown with her husband and dealing with the harshness of the early post-war years, I could still see her outliving "David" to at least 1980 or 1981. But to be honest I think I like the idea of her being the "widow in the shadows" and not overwhelming Margret, though possibly becoming a trusted confidant.
Did you have any thoughts/ideas on this?