DEAR MISS MANNERS: I am marrying a lovely man after three years of dating. He has one sister and one brother. I have two sisters. All of our siblings will be in our wedding party. However, one person is being left out: My fiance’s brother, Max, has a long-term girlfriend, Jenna. The two have been dating since high school and are coming up on 10 years together. Jenna is very smart, funny and driven.