1. If you can establish that she has left her matrimonial home of her own without any valid reason, then she is not entitled to any maintenance. Moreover, she won't get maitenance if she is employed,
2. Ye, she can . The items gifted by you to her are her Streedhan, Period,
3. They shall have to establish that she has been forced out of her matrimonal house or your son is responsible for her such leaving, to claim compensation,
4. If she is employed, she is not entitled to any maintenance. however, your son shall have to contest the said maintenance petition fittingly with evidence,
5. Engage a detective agency to collect evidence for your said allegation,
6.Your son's right course will be to get rid of her and start his life afresh. You can file defamation and file case for filing false case,
7. Nor normally it is between 1/5th to 1/3rd of your son's monthly net earning, if at all she is entitled to get maintenance,
8. Till she becomes capable of maintaining herself or gets remarried.
9. No those gifts are permanently gone,
10. No. Not at all. He has to get the decree of divorce before getting remarried otherwise he will be booked with the charge of bigamy punishable with jail term.