We received an email from my husband's brother that said that only my husband and our son were going to receive an invitation to his son's upcoming wedding.  I am  being excluded as is our daughter.  We are not close to this family, in fact haven't spent any time with them for over 5 years.  (We casually see them at obligatory functions).  I think it is rude to separate husband and wife and brother and sister and that we should simply respond with regrets to the formal invitation.  Am I wrong thinking we should just politely bow out?