Do I tell my ex's family that he has another baby?

My ex and I were together for 6 yrs and we have a 3 1/2 yr old together .Although he doesn't work and doesn't pay child support he does spend allot of time with her, and they have a wonderful bond. He also has a 14 yr old that he gave his rights up to years ago. Now, I have been contacted through facebook by another lady who has a 4 mo old daughter and she claims he is the father. I cant get him to see this child, nor take a paternity test. He also hasnt told his parents about this lady or the baby. Should I go ahead and tell them? I already informed him that our daughter and this new child will grow up knowing each other unless a test proves otherwise. He is an only child and the only child his parents have contact with is my daughter.