Obtain authenticated copies of all loan related documents from lender e.g; Loan Brochure, offer/allurements by lender for loan, loan application, loan approval, loan agreement, loan statement, all communication supplied to borrower with POD etc.
Lender is liable to provide these.
You might have signed clause on Right to set off and lien by banker.
Obtain details of all assets of borrower.
The guarantor as per loan agreement may be liable to pay jointly or severely.
The lender may recover from 3 guarantors.
The guarantors may recover from borrower.
Press the borrower to pay amicably or proceed further as per considered opinion of your own counsel that has examined all docs on record.