If you parent adds your name to CC and then pes are you obligated to pay?

My father in law ped 4/07after putting my husbands name on CC, we did not sign anything but we have had a collector calling for payment. Are we reponsible? he had no posessions other then clothes and pictures, we paid for cremation out of our pockets - my husband is disabled on fixed income we can not afford 5k pay back.