Need advice.

So I'm adopted. I have amazing parents and a wonderful family that I truly love. I recently reconnected with my Birth Dad around late October and finally met him for the first time since I was 2 just after Christmas. It's been amazing. We've both been super open and honest about everything. So my adoptive parents aren't too thrilled about the relationship I have with my birth dad. Now keep in mind he and his wife don't want to replace my parents, but rather just add to my life. They just want me to be happy all around. So yesterday my husband and I were atmy parents house and my mom was washing dishes then suddenly turned around and had the look she only gives when someone is in deep shit with her. She burst into proceeding to tell me that my birth dad is a liar and he only wants to take advantage of me and my husband for various reasons and wants to harm our son......Some back story.... I was removed from the care of my birth parents because of neglect, not on my dad's part, but my mom. My birth mother is mentally disabled, but still capable of making decisions and functioning in society..... She had lied about my dad being physically abusive to her, me and my infant sister at the time...he NEVER was. So reason 2 for being removed. So just a bunch bull. Anyway fast forward back to yesterday, my adoptive parents don't like my birth dad and think he's the villain when he's in fact the victim. They blame him for everything while giving my birth mother a pass because of her handicap. I tried to tell my mom that she's wrong and all the court documents are wrong....it was the early 90's when the police would just believe what they saw instead of doing actual investigating..... I'm currently 30, married and have a son. I would never put my family in any danger. I know all the sides of the story and I believe my birth dad is a good guy. I just wish my adoptive parents would see that. Any suggestions??