In his last novel, or maybe even the last two, it was mentioned that Laz and Lor had paired with Hazel Stone’s grandchildren, the twins. They may have been bi-curious or bisexual, but I doubt they were were lesbians.
Pretty sure I was like 16 or so when I read Heinlein. I’ll be damned I’m going to read that dreck again just to try to prove you wrong. 
Well, geez, why ask us? Use your own Continua Buggy and go ask them. Your best bet is to catch Hilda, Zeb et al. when they’re considering settling down to have babies as I think that’s the only time they visit our continua. Granted, they’ll probably shoot first and ask questions later; might want to send a minion.
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Three of the last four. The Laz-Lor/Cas-Pol quartet is mentioned in Number of the Beast, The Cat Who Walks Through Walls, and To Sail Beyond the Sunset.
Though I don’t think the girls would have understood themselves as bisexual, and certainly not bi-curious, as both those terms have implications of not being the norm. Pansexuality was pretty much the norm among Howards of their era.
Oh, that. They were just manipulating him to get him over his incest taboo, which as 31st (41st? 51st) century Howards they lacked.
Apparently. The bit with Maureen contradicts that, as does Ira’s reluctance to bed Hamadryad.