User blog comment:Otherarrow/Things I have noticed./@comment-1002696-20091130142454

I think the whole Altea Knights x Whitewings is some kind of in joke. You've got:

Frey - Palla, Catria Abel - Est, Palla Cain - Catria, Est

Basically, each Altean Knight supports two sisters and in a way such that each sister appears exactly twice. Abel x Est is an obvious pairing, while it's also hinted in FE3 that Palla also likes Abel. Not sure about Cain.