Fraud In Marriage

My sister got married to a guy in Hyderabad in 2015 but later we realised that that family is full of lies and fraud. The guy claimed to be B.com graduate but in reality isn't even 10th pass. He took a loan of around 3lacs from our family and hasn't returned around 2 lacs from it excluding interest. Some case of 26 lacs rupees fraud is going on against the family(which we came to know later) , and we suspect that it may be a dowry case. what can be done in this case. how to gather admissible proofs against them?