My boyfriend ex's family

I know some people are still friends after they divorce. But my bf ex wife's family and him are still good friends including his ex wife. He's got to go to her house a few days a week to care for his special needs daughter. But any time there's a problem or get together etc. he's always invited. Is this right for him to be so close to them. I feel that part of his life is his past and it should stay his past unless it deals with his daughter. Am I right to think this? Please give me your thoughts.