We are having a small wedding (approximately 50 people) and we have decided we only want one attendant each. My only sister (only sibling) is going to be my maid of honour and my fiance's only brother will be his best man. That leaves out one sibling, my fiance's sister. Neither of us are that close to her, but I kind of feel badly excluding her. What is the rule here? We really didn't want a big wedding party but I don't want to make a big faux pas.