I just think where its effectiveness gets brought into question is the fact that we don’t get any of this jealousy stuff until, ironically enough, after we have already found out that Luke and Leia are twins.
I’d say the problem is that Han & Leia fell in love and told each other so in the previous film and again at the beginning of this one. The jealousy stuff is silly in RotJ. Han & Leia are in love at the end of ESB and the beginning of RotJ. Then, suddenly, Han worries that Leia is gonna go for Luke OUT OF NOWHERE AND BASED ON NOTHING!