bank defaulter case

My father-in-law owned a company . He took a loan in 1989 from a co-op. bank on the name of his company. But after some time , because of lack of money , he was unable to pay to the bank. (As per bank's advice he mortgaged one flat and sub-mortgaged other flat.) Bank had filed the case, but nothing was proceed further due to absence of parties. After the big losses in the business, he wind up all company and came to us. He told us that , in the mortgaged flat , one of my brother-in-law and his family is staying for all this years by taking some kind of stay order. But there is no any tenant agreement or any kind of rent receipt involved. The sub-mortgaged flat was sold to one of his friend, but as original papers were with the bank, that flat is not transferred to that person's name. Now he wants it to transfer. And me And my husband wants to settle the loan. How it can be done ? What should I do do take flats possession from my relatives who are illegally living there for 20-23 years.