My 10 year grandson hits, pushes, kicks & spits on my 7 year old grand-daughter. He is ADHD. When she complains, he always says it’s not his fault that it was a accident or she got in the way either when he was moving his arms or spitting although last week he did admit that she was aggravating him so he hit her. 
He also tells stories (lies). I’ve tried everything from talking to him about the problem, talking to him in a positive focusing on him & how great he is, taking away tv time to recently spanking him. Nothing helps. I do correct her if she is aggravating him, but the main point I’m trying to make with him is it is NEVER ACCEPTABLE to hit a girl. NEVER! 
I’ve told him if she is aggravating him to please come tell me & I will handle the situation. 
Just yesterday he stabbed her with a pencil leaving a small bruise & scratches on her back. 
He’s a good boy & is super intelligent excelling in his school work. A very loving & sweet child other than this issue. When I have taken tv or electronics away from him, he gets so mad & gives me horrible looks & will tell me he is mad. Gripping his fist like he’d want to hit me. I am at the end of my wits. 
Both parents are divorced & neither really focus on the kids. I have them 2-3 nights a week & my husband & I spend more time with them than their parents. We try to be a positive influence on them since their parents doesn’t make the kids their priority. We spend time with them, going for walks & etc.. I know this was long & apologize. Please any advice is needed.