Joint settlement by creditors wit 2 separate Pvt ltd company

We have two companies A and B. Both private limited companies with separate identities, partially having some common directors but no inter relation such to share holding, inter corporate debt etc. Company A owes bank 100 Rs. Company B owes bank 300 Rs. Bank wants to Dona single agreement for settlement of dues for both companies together. Can it be legally done , because both have individual debts to the bank and no joint agreement of takeover of debts and what happens if one company fulfills his part of the debt obligations but the other company fails