Would you help your sister's cheating husband?

I made a post on here not too long ago about my sister who I'm super close with getting arrested. She found out her husband was cheating on him and she beat him with a bat in front of my 14 year old nephew and my nephew tried to stop her but he couldn't. Then when she knocked him out she tried to assault him with the bat down there and she got an SA charge along with her other charges. My nephew is staying with me because his dad had been sent to the ICU in critical condition. My sister has been hurt that my nephew refuses to speak to her and the last time they spoke was yesterday with him telling her she's dead to him. She's most likely just gonna take a plea deal but the situation going on now is my nephew's dad is now conscious. He's talking and should be okay. He won't be released right away and will have to have some physical therapy. My nephew just wants to go back home with his dad. His dad most likely even with physical therapy won't be able to care for the home and everything well for a long bit. My question is, if you were in my situation, when your nephew went back with his dad would you help around the house and/or with dinner. Because on one hand helping him is helping my nephew. On the other hand my sister is my best friend and that would be betraying her. Me and his dad haven't really talked. I've let my nephew stay at the hospital with him until visitation hours were over and I know he's going through a lot. We are looking into therapy for him. But in my sister would you help the person who cheated on and destroyed your sister?

Edit: I know my nephew is old enough to know these things. He's just really mentally messed up right now and the worries I and other family was having was him having to take care of his dad for a bit while keeping up with the house.

Edit2: She's not gonna be able to avoid prison unfortunately. She has an assault with a deadly weapon charge, child endangered, sexual assault, etc. It's why she's pleading guilty for a lighter sentence. I just hate hurting her because she's already hurt that my nephew refuses to speak to her and told her she's dead to him. And I understand people point on my last post and I need to support my nephew wanted to sever his relationship with my sister. I just hate seeing her hurting.