Alle Kunst ist der Freude gewidmet

And the the fact that "They should be the last of their family" kinda rules out any other relatives

That too, but FE has played kind of loose with that. I mean, Marth and Elice are supposedly the last of their dynasty, but they turn out to have an family of cousins ruling the next nation over.

Besides, none of the FE8 mothers even got NAMES, which is pretty... sad.

I find the (seemingly) general belief that nobody ever remarries in ffs very strange (and not exactly fair).

I think it has a lot to do with ideas of "happily ever after," but I agree it's odd and a little depressing at times.