Making Rey Luke’s daughter would be the cleanest and simplest way to go, especially since it’s very nearly spoken in dialogue between Maz and Rey in TFA.
Anyone else and you would need new scenes that didn’t exist.
I guess you’re right, there’s enough dialogue/footage to make it plausible
Luke’s family disappearing (with his wife dying and his daughter trapped on Jakku) could be perfectly used as the reason of why he is a broken man who lost faith in himself during the ST and even thinks briefly about killing his own nephew after sensing Ben’s dark thoughts