Ok, don't shoot me but I think you should leave it. That's your DP's son and I think if he makes a decision regarding his son than nobody should come between that as long as its not harmful. What does your DSS mum think about it? As long as it's not causing any friction or problems for the little boy, what harm is it doing? If it's causing problems with DSS mum, then they should really work it out, but otherwise it's not hurting anyone. He's lucky to have so many people caring for him