Hi
First the women should relocate to Mumbai and file the following:
a) divorce petition against her husband and also ask for child custody. Mother will normally be granted custody of the girl children.
b) Domestic violence.
Till such time the child custody and divorce proceedings are complete with a court decree, live in relationships should be avoided. however she can stay in an apartment close by and you can provide her with all support required by her during this traumatic phase of her life.
The rationale for recommending avoidance of live in relationship is based on the fact that the husband should not accuse her and you of bigamy(which is a crime in indian law).
Normally men resist mutual consent divorce(Mutual consent divorce is the fastest way to get a divorce.
However men relent later and accept MCD when subtle pressure levers( suits) such as domestic violence are foisted by the women in addition to Divorce proceedings and the pressure becomes too much for men too handle. Added to the pressure of multiple suits against men, the self realization that happens to the man when he realizes that he has lost the child and woman because of his own perils will force men towards Mutual consent divorce.
If you can plan all of your next steps after consulting a lawyer and prepare a time bound action plan for each of your next steps, you and the woman can come safely out of this issue without any hassles and within 6 months.
hope this helps.