Would you go against a parent's wishes to help their adult child out of a bad situation (Read description fully before answering please)?

I actually have this happening in two different cases. My younger brother treats his daughter like a slave. She is expected to keep the house clean, watch her special needs sister, go to school (online classes) and she is also working nearly 30 hours a week. When I say slave I mean, he refuses to do the work at all including taking care of his own special needs daughter. He refused to let my niece (she is 17) come over to see our new puppy because he didn't want to watch his special needs daughter by himself. He also makes her do stuff like massage his feet, bring him dinner and give him money from her paycheck to buy him fast food. There is more than just that, but these are just examples.

When she is 18 she wants to move in with my wife and I so she can get away from it and focus on school and having a life.

My friend (21) also has a very similar situation where her father actually bugs her apartment (he sometimes stays there and pays rent since she is a full time student) to listen in on her conversations. He says he is only paying for her college so she becomes a doctor where he can then retire and have her support him financially for the rest of his life. She isn't even sure she even wants to be a doctor and has major medical issues that her parents ignored growing up that could have been fixed when she was younger. Her mom is not better honestly. I have sort of unofficially adopted her and she does things like movie nights with me and my family (our kids see her as an older sister), but mostly I just try to help her build confidence in standing up for herself.

Given the situations, would you help or stay out of it?
I would help in the first case, but NOT the second.
I would NOT help in the first case, but I would help in the second.
I would help in both cases in any way I could.
I would stay out of both situations and let their parents decide what is best for them even if it is detrimental to them.
Other (Please explain)
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Would you go against a parent's wishes to help their adult child out of a bad situation (Read description fully before answering please)?
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