i totally agree on her purpose in the story. but let's say that on qaf it's real. they're real people and we're just seeing the bits that tell the poignant moments of their lives that move the individual stories forward and how they, as family, intertwine. well, a threesome with brian and justin wouldn't be part of it. not because it's sex and therefore not poignant, but because (since it wasn't in the story and i absolutely do not think the writers were tryhing to leave a cliff hanger there. i think it was meant to mean nothning and be nothing for the purpose of the episode), but there's nothing out of character about it in my opinion for justin and brian to have an experience with her. not at all. besides, people do things that are out of character sometimes. so i am just coming from the vantage point that these people are real, and we only get to see some of their lives and we guess at the rest.
i don't think that would be a bad guess, to guess that sex or rubbings or more serious flirtations went on between the three of them.
if i were to write it myself, it would be just them getting in a huddle in the kitchen rubbing up against each other, maybe leda would tug on brian's hair and bit justin's ear while brian and justin made out. maybe she would even stick a thigh between justin's legs. to me. with the way these three live their sex lives i don't think that those actions would be taken much more seriously than a verbal joke. like. they'd be giggling. then brian and justin would go home fuck their brains out just the two of them.