George V m. Mary of Teck
1) Alexandra, Princess Royal and Duchess of Windsor (1894-1972) m. Paul Blobel (1894-1951) [1]
2) Mary III of the United Kingdom (1895-1952) m. James Reid (1890-1975)
3) Victoria (1897-1965) m. Henry Lascelles (1882-1947)
4) Adelaide (1900-1974) m. Edward Cavendish (1895-1950)
5) Charlotte (1902-1942) m. Francis Manners (1897-1972)
6) Augusta (1905-1919) never married
[1] I figure this should be scandalous enough to force her to abdicate, imagining the Queen of UK married to a proud Nazi would have Parliament shitting bricks...
firstly, it's cute that you think Alexandra would be allowed to remain single until 1931 (when Blobel joined the Nazi party). She's the heiress to the British throne, she's marrying in the 1910s- 1920 is the latest. So unless she meets Blobel before then- in which case he won't become a Nazi since why would he be in Germany bitter about losing his job if he's the consort of the British heiress?
Secondly, given that Edward VIII's sterility resulted from a case of mumps he contracted in France while on active duty IIRC, Alexandra won't have the same problem (why? mumps doesn't affect little girls the same as it does little boys AIUI).
So, we'd have a girl- Victoria II (she'd be named after her great-grandma, not her grandma- as was OTL Mary, Princess Royal) or Mary III- who marries between 1914-1920. She'd be too old for the son of Max of Baden (Max's daughter was the premier candidate being considered for Edward VIII when war broke out), but Max's brother-in-law, Ernst August of Hannover (who married the Kaiser's daughter) could easily be considered (especially if his brother doesn't die in a car crash in 1912). Failing them, there wouldn't be a shortage of German princes (Alexander of Greece. Mossy of Prussia's Kassel sons (two of whom were considered for Queen Wilhelmina, etc etc) vying for the Princess Royal's hand in 1910 when her father becomes king.
And
even if they decide to go domestic, godalone knows there are enough domesticated royals. Dolly of Teck's son. Dickie Mountbatten- dear God he'd be ambitious enough to try- his brother, George. Dickie's cousins, the sons of Princess Beatrice.