Marg, at some point in the movie, when the son and his friends discover gay male porn in the moms' bedroom, he asks why and Jules says something about sexuality being complicated. For Jules, who in the end, I thought was rather unkind to Paul says she's gay and I believe it, but it is obvious that she's attracted to men, at least under some circumstances. I would say that she's bi, but loves a woman and has chosen that love over another.
I thought all of the performances were excellent. The Kids Are All Right is not a 'big' film but I think it's got a 'big' idea, summed up in the title.
BTW, I thought that Annette Bening was very brave to portray a character I found to be not particularly likable.