His Wife Wants to Have Sex With Her BROTHER?

This story hits about 9.9 on my weird-sh*t-o-meter. Throw in some aliens and it would top out…

My wife and I have been in an open marriage for five years. On the whole, our relationship has been uncommonly open and supportive; we both strive to encourage one another to explore, and even playfully push the limits, romantically and sexually.

For as long as I have known her, my wife has been interested in “incest” role play. While it isn’t my cup of tea exactly, I have been willing and happy to support her in her exploration of this kind of fantasy and role-play. Often, she will have me dress up as her father, wear his cologne, etc., while she will wear her “high school” clothes.

Recently, though, things have started to move in an uncomfortable direction for me. My wife is very close with her older brother, who is also bi, and with whom we often speak very openly about sex and sexuality. A few nights ago, and after a few drinks, my wife got to talking fairly explicitly about some of the “family” role-playing that she and I are into, and her brother—who I thought would be kinda horrified—was not only entirely supportive, but vaguely expressed interest in exploring this kink with us. When we got home, I expected my wife to make it clear that her brother ever joining us in the bedroom was entirely off the table, but instead she seemed to think it was a really good idea. In principle I don’t have a problem with the idea. While, like I said, I am not that into the “incest” element of my wife’s (and, I guess, her brother’s) fantasy, I am happy to play along if it makes her (and him) happy. My wife and I have also enjoyed group sex, and so that isn’t the problem either. I guess at bottom, I am just worried about how this could affect my relationship with my brother-in-law. Is there a way for me to make this happen, without it getting weird?