I think it's self-defense, protecting his children. This is the father's nature, and it is also his nature. Anyone would do that. Your sister doesn't care about family first. Don't use illness as a cover. Maybe she has a problem with you and will take it out on the children. It can't be like this. She'll become her nephew. Ask you if you have any questions. If you don't kick her and stop her, people will die and the consequences will be serious. You handled it well.