Ok, so there are identical twins and fraternal twins, why can’t there be…uh…some term for twins born two years apart?
Or maybe they’re half-siblings. Vintage 1977-canon taste with the same incest flavor!
Seriously though, GL first decided that Leia would hook up with Han rather than Luke in late '77 – the very same time that he began thinking Luke’s sister should appear as a new character in a future SW film.
And virtually all of Ralph McQuarrie’s concept art from the first film shows Luke and Leia with identical blond bowl haircuts. Join the dots.