Ok... and?
Fire Emblem is a work of fiction, it’s fantasy. It doesn’t have to follow rules that older societies followed just because it’s loosely based on that time period. Same-sex marriage was in Fates and Three Houses and no characters in game gave a shit. And what’s wrong with have LGBT characters in things? If it were to be implemented into Genealogy it would probably be handled the same way the last two games handled it, an option. If you want to make everyone straight, make everyone straight! No ones going to stop you.