I don't agree with the idea of first-degree relatives having an intimate/sexual relationship with the same person, but at the end of the day it's none of my business what people decide to do as long as it makes them happy and everyone involved is agreeable to it.
Personally I think you should let this one go because it would cause more harm than good. Especially since it seems as though you and your wife at worst have issues in your marriage that should be addressed before you decide to "go poly", and at best, have marginally discussed poly but not agreed to try it yet. It is a big enough challenge to "try" poly even when neither partner has someone else they are interested in, let alone when they "try" poly BECAUSE one of them is interested in someone else. Imagine how the problems might be compounded because you've decided you want a relationship with her SISTER of all people. This isn't a Mormon family or some cult where this kind of thing goes on all the time, and just because "other cultures" do this (sisters marrying/sharing the same man), that doesn't necessarily make it okay.
I'll probably get an ass-whopping for being "judgmental", but if other people disagree with me, let THEM say so. I'm telling you my own viewpoint on this sort of thing. There are probably other people here who will tell you that this sounds like a peachy-keen idea and that you should go for it.
Last edited by NeonKaos; 12-28-2010 at 08:01 PM.