Ephraim is protective of his dear sister, what things would he do if Eirika and summoner in a relationship, and the reverse as well, would Eirika give Ephraim dating advice? I think so
Eirika reacting to Ephraim in a relationship with the Summoner
-She would do her best to help him with dates and presents.
-Eirika knows how much of a disaster Ephraim can be so at least until he figures it out, she will be the one to guide him through on how to treat you. Though he doesn’t always listen.
-She helps pick out nice clothes for him to wear and tells him things that he should consider saying.
-She is very supportive of you two like the good sister she is, and she wants her brother to be happy.
Ephraim
-He’d be very wary of you. It doesn’t how friendly or sweet you are at first he will be upset that he now has to worry about someone breaking Eirika’s heart.
-Though he will have to back off at her insistence.
-Though he wants to be a helpful brother, he can’t really give her any dating advice at all. He is pretty much clueless at it.
-Ephraim trusts his sister and knows that if she really likes you and you like her then it will turn out okay.