Disowning a child is not a legal concept, and there are no rules.
Commonly, people refer to a parent writing an adult child out of his/her will as disowning a child. In this case, yes, the parent could write them out and write them back in again as often as they want.
In most countries, parents cannot legally disown their adult child in the sense of completely severing legal ties, such as disinheritance. However, parents can choose to have no contact or relationship with their adult child, which is not the same as disowning them in a legal sense.
The closest thing you could do would be to get a restraining order. Because he/she is a bro/sis you can not "disown". disowning refers to taking someone out of your will. if if you want to. you could do that in addition. but moving away would be the closest thing to "disowning.
not without child's consent..
No. Your parents are legally responsible for you.
No, when you turn 18 you are legally an adult. Regardless if you are living with your parents are not you are granted full citizenship at that age.
No, they are not legally required to do so. The adult is responsible for their own life.
Yes they can, welcome to being an adult.
Legally - an adult. If you are a minor - your parents or guardian would have to do it.
drop him of at a foster home
Many places allow you to legally "divorce" your parents or children. If your son is legally an adult than you should be able to do this, if not, don't bother.
Yes. You just have to write in your will that your adult child gets NOTHING.
Parents are liable for their children until they become legally adult.