Children getting treated differently

Gabby

I have 2 babys & pregnant. I have a 2yr old and 5month old . My 5month old is my boyfriends first child his moms first grand baby .. his mom treats my children completely differently. She never wants to spend time with my son now that my daughter is here . &he clearly can tell . So lately I've been telling them either u get both &spend time with both or you dont get the baby period . It's not fair to my son .. yes sometimes without him is fine but the past 2 months it's just about her.. am I wrong ? My boyfriend treats both my kids equally.. but he refuses to stick up to his mama I have to .. I hope this all makes sense