I'm afraid it might get complicated but it may help
My sister called me today to tell me that her and her DH are having some issues in the bedroom. Her and I are really close and I have told her about all of my bedroom play time. She asked me if I could have a threesome with them since her DH had always dreamed about her with another woman. She doesn't trust anyone other than me because she knows I don't really have an interest in her DH at all (not that he is bad looking or anything, just not my type). Do you think I should do it to help spice up their sex life?