Thanks for replying Ygirl, and thanks for the links.
Oh, I know it doesn't matter, as you say, but it was just that I had such a visceral reaction to the idea of sisters sharing and then wondered if that was MY issue, IYSWIM.
I can totally get polyamory but could never consider it with my sister <eew>.
I thought I'd run it by some real polys (as opposed to weirdy made up ones
) and see what the consensus was.