tenancy deposits

Tenancy Deposits

Hi, I acted as guarantor for a house my son rented with friends. an agent organised the let. All the parents submitted their despots and guarantor forms to the agent . It says on the first page of the contract that the tenancy was arranged by Robertson Smith & Kempson Ltd 15 the Mall W5. They passed the deposit to the Landlord who made her own arrangements for registering the deposits with DPS . The Landlord is refusing to repay the deposit without unreasonable deductions since the tenancy ended on 3rd September. The deposit was registered with DPS on the tenancy start date. Only the lead tenant was provided with the details of the scheme not the other 3 tenants or any of the 4 sets of parents who all made individual guarantees and payments to the letting agent. Please can you advise how strong our legal position is now for recovering our deposits.