Maintenance if wife is earning more than husband and having a girl child.

My Sister got married in Nov 16. She had a monthly salary of 30k at the time of marriage,which was later incremented to 40k. We were told that the guy earns 50k/month. After marriage, from the very first month my sister was emontionally harrassed by her in laws. Her mother in law and her husband asked for all of her salary if she wants to stay in house. Torturing her emotionally, he took all her net banking passwords and control over her debit cards and credit cards and used those for himself. After 4 months of marriage,They took a Car in her name with a car loan of 8 lac with emi of 12k/month. Just for the sake of maintaining her relation she agreed to all their demands.They also took a personal loan of 2 lacs in her name with a monthly emi of 7k. Later in july 17, They applied for a home loan of in DHFL in the name my sister which was sanctioned by DHFL but by that time she understood all their intentions and didn't let them take that loan. She was sent to her parents home after that when she was 6 months pregnant. On mutual discussions, she was sent back to her matrimonial home in nov 17 and she gave birth to a girl child in dec. later in jan 18, she was again sent back to her parents home with a statement that 'she is of no use to them'. Its been 3 months she is living with us and paying a monthly emi of 19k. The possession of car is with them. All the meetings and panchayats we have done are now worthless.Now, from some external sources, we get to know he only earns 20-25k/month. if we go to court is there any way we can prove that they were doing fraud with us? Can my sister claim maintenance from him? Should we take posession of car with the help of police first?