@King_Noticer @DEERBLOOD @d0c40r0 If it makes you feel any better, the game tells you on S supporting one of Corrin's blood-related sisters (or brothers I guess) that actually Corrin's mom already had Corrin before showing up in Hoshido and you're not blood related at all. You actually betrayed your adoptive family for a different adoptive family, not your blood relatives.
Oh, and as you find out in Revelation, Azura and Corrin are cousins. Yes, Corrin can marry Azura. Yes, the mechanics are set up to make Azura the easiest marriage option in Revelation.