u/Len1177

https://preview.redd.it/4hm9qu4bmmzg1.png?width=736&format=png&auto=webp&s=bd7f9705105bd41f2cf0355631eaeca7d20bf71b

https://preview.redd.it/tvec4jmbmmzg1.png?width=789&format=png&auto=webp&s=cd4a57e767a722168fb9aa675c4a5664a8528ac1

Honestly, I did nothing involving the Tyrells or the Arryns; I didn't even arrange marriages within my own family that could have affected the line of succession. They were simply replaced. I checked, and they haven't even gone extinct; in fact, the Arryns are currently at war to reclaim their title. The Tyrells, however, simply accepted their fate and became a minor house; they don't even have a faction opposing the new ruling house. I don't use console commands or similar cheats, so I reloaded my game and checked my oldest available save files. I couldn't pinpoint exactly when the issue with the Tyrells occurred, but I managed to figure out what happened with the Arryns. It turns out that, for some reason, Lord Arryn had a daughter and a son. Inexplicably, he married his daughter off to a member of a relatively minor house, while betrothing his son to a Lannister. However, his son passed away, and shortly thereafter, Lord Arryn himself died. Instead of the inheritance passing to one of his brothers, it fell to his daughter. She already had two children; the eldest of them became her heir, even though her younger children—born subsequently—were raised as Arryns, while the older ones were not. Since all her children were the product of a single marriage, upon Lady Arryn's death, the inheritance passed to her eldest son—who was not an Arryn. Something similar likely happened with the Tyrells; in fact, I checked, and the Tyrell line has practically gone extinct. Only four Tyrells remain: a single male (who is still an infant), two elderly women, and a third woman who is married to the Prince of Dorne. Therefore, the Tyrells are, for all intents and purposes, extinct. The same situation applies to the Greyjoys, although they haven't been replaced yet. They have only three living males left: one who already has "one foot in the grave," another—aged 40—with a wife of about 30, and the latter's only son, who is homosexual. Consequently, I do not foresee a very promising future for the Greyjoys.