Am I a jerk?

Or is it that I don't want to be controlling and interfering with others.
I don't have the highest regard for my brother and I believe with good reason But he seems to in his own way care about my sister and me as well as my father. The only problem with his caring is that it means that he thinks he is always right about everything and we should do what he says.
he has been going over to my sisters again and she can't tell him no or not let him in tho she does not like what he is doing in telling her how to act and eat and whatever. But she is lonely and puts up with him to have him visit. but I can see him taking advantage of her at some point.
I don't have any say in anything and it is only my own feelings about it. I feel sorry for her having to learn to live on her own, which she is doing very well tho needs some reminders, but I dont see anything good coming out of letting him back into her life and controlling it and telling her what to do and how to do it. She needs to learn to be on her own and taking care of herself as much as she can. My brother continues to see her as being a three year old, incapable of caring for herself and so when he is around she acts like this.
I'm not sure what to do about it.