Today I double check with civil lawyer. She suggests

that my mom should file devoice with him. The lawyer said that as long as my mom still have legal relationship with him, she has to be responsible for all his medical expense,even my dad is abusing the system. Also they have lived separately for over 8 years,it is enough to claim a devoice.
It is really painful to bring this case on here. What is the meaning of family? I have no idea.
I truly appreciate all of you who gave concern and encouragement. May God bless all of us.