Boyfriend's ex still close with his family... 😞

I've been dating my boyfriend for over a year and a half now. We have our own place together and are expecting a little girl in May. We are extremely serious and very happy together. To this day I have not once met any of his family because his ex is at all of his family gatherings and holidays and still talks to them. They do have two kids together - but okay... So? That is not an excuse to steal someone else's family. He would be more than willing to take his own kids himself to visit HIS family just like my parents did when they split up when I was young. Not one of his family members ask about our daughter or even care. Last night I asked him if he could go through his family and see who he wanted to invite to our baby shower because I'd love to have some of his family be involved with our baby. After all, this is her family too now. But when we were looking on Facebook we saw his ex write to his Aunt "Happy Birthday Aunt Carol, I love you!" Just recently. His dad, step mom, and sister (along with everyone else) all still see her and hang out with HER and he hasn't seen them since they broke up because she completely took over his family and he feels that if they can't be on his side and support the fact that he no longer wanted to be with her like a family should, then he wants nothing to do with his family. Now my daughter will grow up not knowing her other side of the family or her brother and sister because she has been shunned because of his ex. No one has ever tried to get to know me, ask about his new daughter, or even care. To me this is unacceptable. My poor baby girl. She is raising his two kids to not want anything to do with their sister either. He was so excited to tell them they were getting a new sibling and they were just like yeah so? 
It just hurts. Has anyone else been in this situation or have any advice? I just want my daughter to have both sides of her family.