Can my parents legally make me stay home?
No. They simply are not responsible for you anymore. If any harm is done to you to make you stay than others charges such as battery can be considered. So no, parents can not hold their adult children against their will.
Can I lose custody if I live with my parents?
Each Parent's Living Situation The location of the home in relation to the child's school and activities will be a factor in the case. If one parent lives further away from everything the child knows, that could be a mark against that parent getting custody of the child.
How long does a parent have to be gone for it to be considered abandonment?
Abandonment and Termination If a child has been left with a non-parent for six months or more with no contact or support, that constitutes abandonment.