Several years ago my brothers and I (5 but only 4 went) decided to do a MAN CAMP with Dad. My sister was NOT welcome...and neither was her husband. It was ONLY for the men in our family. The youngest nephew was 12 yrs old, so we did NOT allow them either, because we had no desire to entertain kids. When he turned 16 yrs old, he and the other nephews then became part of MAN CAMP WEEKEND. One nephew, who lives with a man, took it personal when we said "no" to his other-half. SORRY, but spouses are NOT welcome, even if your "Spouse" happens to be male....get over it. We have never invited our brother-in-law, we will not invite a nephew-in-law. Every person there was born with the same last name (except my step-son)...that is the way we like it.
Set rules, stick by them. That simple.