AITA for asking my in laws to not give money to just one of our kids

The eldest girl has always been my in laws favorite. My middle child is a boy. In the past, my in laws have shown favoritism to my daughter, which I have voiced that I’m totally against. They have given gifts/clothes to her and not him, my sister in law has invited my daughter to stay the night at her place and not him. (she has kids of her own) Her son (my sons cousin) has even told my son that he is grandma and grandpas least favorite.

Most recently they were over and gave cash to her and not my son. Well, he found out and was pretty upset. I asked them to either give them both something or nothing at all and they got upset. Since then, they’ve ghosted me and told my wife that I’m treating them like shxt and are pissed.

How on Earth would you deal with this? It’s upsetting to me how they can’t understand what should, in my opinion, be common sense. This is about my son and they’re more concerned about themselves.