Sister trying to parent my kids.

So yesterday my 8 year old apparently hit my nephew with a zip tie (yes a zip tie) and my 13 nephew didn't say anything about it bc they were outside playing in the yard and both the boys had came back inside and everything was normal then when my nephew and my sister (his mom) went to go to the dollar general he told her what happened and she came back to the house and scolded my son. Not only did she take my sons phone (it's just an old phone of my mom's that he plays games on) but she told him that he isn't allowed to play on his Xbox.. I was at work and didn't know what happened with any of this til my sister called me and told me she took my son's phone and that he wasn't allowed on his Xbox bc of what he did.. Now this happened at my mother's home bc that's where I'm staying til my apartment is ready and my niece and nephew stay there but my sister doesn't.. I was like wtf.. It made me upset bc that's my kid not hers and this is literally the first time my son has done anything to my nephew but my nephew is always bullying my son (yelling and hitting him) and when I tell my sister she just says "oh they're just boys what you expect".. She also allows my nephew to talk back To her and when he gets in trouble in school she always acts like it's the teachers that are the problem. She should have told me what my son did and I would have taken care of it but no she wants to try and parent my kid.. I pay the light bill and internet so I turned the internet off on my niece and nephews devices (cell phones and game systems) and now my mom is telling me I should turn it back on bc it's just gonna start crap but honestly I don't care.. If my son is allowed to be punished by their mother then I'm going to be petty. I'm tired of my nephew getting away with everything while my sister is a constant b hole to my kids.. If my 8 or 3 year old does anything she doesn't like she Yells at them and I'm sick of it! I can't wait for my apartment to be ready so I can get away from all these people!

Side note.. Nor my sister or mom saw my son hit my nephew with this zip tie but apparently he had a red mark..

My sister lives with her bf in a small 2 bedroom trailer. They make more than enough to get a bigger place for themselves and the kids. My sister owns her own home but it had to be gutted due to mold and she hasn't done anything with it since and it's been about 5 years since then.. I honestly feel like she doesn't want to deal with her kid's so she makes excuses as to why she doesn't get her own place for her, her bf and the kids.. My niece will be moving in with me bc she doesn't like her moms bf and she's tired of living with my mom. My sister is the type to buy her kids affection. She comes over to "spend time with them" for about 3 hours after work and that's about it.. She doesn't spend real time with them or do anything with them.. I feel like it's affected her kids mental health especially since their father died of a heart attack 4 years ago so their mom is all they have. She is neglectful and that's all there is to it. I'm thankful my niece isn't like my nephew. His attitude is so bad I don't even like being around him.. It's bad.