1) your son and daughter in law should visit a marriage counsellor to resolve the issue .
2) if daughter in law refuses to mend her ways your son should file for divorce on grounds of mental cruelty
3) in the event any false domestic violence case is filed contest it on merits .
4) if daughter in law files 498A case for dowry harassment obtain bail from court and contest it on merits
5) custody of minor grand son would be awarded to mother ,. father will get visitation rights .
6) daughter in law can in addition seek maintenance for herslef and the child