Actually I think what it "feel like" to the couple in question (the LW and her domestic partner/common-law-spouse/what­ever) is the CENTRAL issue here. She feels like making him dance like a trained monkey because his younger brother had a church wedding before he did suggests that his relationship to her has no meaning. I would find it insulting if my partner's sister told me I'm not part of his family because we're not married, and I'm happy she doesn't feel that way. I would have no problem telling her directly that I thought her attitude was offensive, though, so I guess I'm a bit more direct about things than the LW. The LW's partner should tell his brother's fiance he won't be submitting to this ritual because it'll be much worse to piss off the woman who shares a home with him than the one who only shares a family tie to his brother.