Owner issues with car?

hi, my hubby and i bought a car from his sister which was in his step fathers name. it was supposed to be transferred into my dads name as its a shared car. unfortunitly his step dad never recived the v5, and because he owned the car for a year and never botherd his backside to tel them he never got it we have to pay for it. (we didnt know this when we bought it we where told it was in the house and hed ("DIG IT OUT") . hes since called the dvla and had a letter confirming hes no longer the keeper. he says he gave the dvla my dads details as the new keeper but my dad hasnt recieved a v5. the tax runs out at the end on june, and i dont want to fill in the form for hi as new keeper if he is the registered keeper. is it possible for a car in the uk to be unregistered? how can we find out who owns it now? its a strange problem but i cant find the anwser online?