I have a younger brother who is getting married soon. I am one of three siblings; there are two sisters and our younger brother. We have these family friends (as in our parents are friends with their parents and we children are with their children) with whom we are somewhat close, kind of like an intermediate friendship. They are all married and our brother is the last one of the sex marry. They all thereby obviously have spouses. My brother has decided to not invite any of their spouses, just the parents and children. The reason for this is because at their weddings, he was not given the option of a plus 1. He was just sent on the same card as my parents because he still lives at home because he believes that living with someone before marriage is a sin. I keep telling him that it is wrong to no invite a married couple but he is very headstrong and keeps going on about fairness, reciprocity etc... He points out to my sister and me that he didn't try to interfere with our weddings and fair enough, he didn't. But we just think that he should invite them all. His fiancé has two couples on her side who did the same thing to her and she is also not inviting them.  I just want to point out that my brother is a very nice person, has a generous heart and is a true Christian, not someone who just cherry picks to suit their agenda. Just on this I think that he is totally wrong and nobody can through to him. What should I do? What can I do? Any help at all would be much appreciated.