Long story short my stepson is 11 , hes never liked me and I understand it’s hard as I’m not his dad , I always tried to be there for him , we had good days and not so good days , but I never took it personal as I understand he’s just a kid ... I knew he was bullying his step sister who has a disability ... I tried to point it out but my partner whom I adore and she adores me didn’t take it so seriously at the time ... the only time we argued was about his behaviour which was totally spoilt and treating his mother like a servant ... then our daughter arrived and everything seemed fine ... but when she got to a year and a half old I started to get paranoid when he was around her ... my instincts telling me something wasn’t right as she would trip and fall etc if he was near ... it was holidays so I took him to the park for four days that week , then he went to private football training and the same day he went to the Cinema ... so he got everything for him all attention ... that night my wife and him and our toddler were playing out the back .. she went to get some washing and then my stepson did a quick check to see if anyone was looking and picked up a rugby ball and smashed it towards her head .. then pushed past her again to get it .. I was upstairs looking out the window to see if he would do anything and I was right ... so I banged the window and stopped him from hurting her again .. she was 1.5 years old and he was 11 .. obviously I went mad and his mother the same grounded punishment and I knew my instincts were right .. this was 3 months ago .. last month I caught him again banging her car seat when his mother got out but then he pretended to be looking after her when his mother got back in the car grounded again .. thankfully his mother has now decided to contact support groups and get him someone to talk to ... some of her family said this thoo was normal sibling rivalry ? I just don’t think so as the age gap is terrible ... I’m not speaking to him and don’t trust him at all .. because if his sneaky ways and my main priority right now is making sure when our backs are turned he does not try to hurt them .. at the minute I am consumed with resentment and anxious ... any suggestions on what I can and should do please ?