What is the name of your state (only U.S. law)? CA My sitster lives in CA and wants to leave her husband. They are living with his parents right now and she is considering leaving and going to our mom's house for a week or more. She will probably not return and then seek a divorce. I know her husband will seek custody. Is her leaving considered abandonment and will that in turn grant him full custody if that is what he is after? Any advise?
Like everyone has told you, if she leaves the children with dad and the paternal grandparents it is very likely that dad would end up with primary custody.
If your mother does not also live in CA and she leaves and takes the children out of state, it is also very likely that dad would end up with primary custody.
If your mother lives in the same area, and she leaves and takes the children with her, then her odds of primary custody are greater.
If she leaves with the children, stays in the area, files for divorce and permission to relocate with the children, then she might have a shot at getting permission to relocate with them.