Any advice on this?

Looking for some advice/opinions. My 7 year old is autistic and is very upset at his uncle and future aunt to the point where he won’t talk to them because they are not including him in there wedding like he hoped for and like we were led on to believe. I’m kind of upset for him and don’t really know what to tell him. He is extremely close to his uncle (my brother in law) and his future aunt, so we’re all kind of shocked. Even my mother in law is disappointed. My son is their first nephew. They are getting married next year, my brother in law was in our wedding and was my husbands best man a few years ago. If they had kids we would have had them in our wedding in a heartbeat but they don’t have kids. We don’t think my brother in law is even going to ask my husband at this point to be his best man because it seems to only be her family getting asked to participate in the wedding. They just asked her niece and nephew to be the flower girl and ring bearer. My son found out and he is very upset. I’m not sure how to approach this, I get that it is there wedding and there day but we are very dumbfounded because we were led on by them to believe that our son would be included as well, and that they were figuring out a way to ask him. Am I wrong in asking them to explain to their nephew (my son) why he isn’t included? Because I don’t know that answer myself. We have never ever had problems with them, we are all very close. They just kinda dropped a bomb on us and it upset my mother in law as well. And I feel so bad for her because she hasn’t been included in anything yet and this is her son getting married. It doesn’t seem like he has a say so in his own wedding.