Here we have to see that at the time of granting home loan, whether the son was taken as co-applicant in the case to make eligible for the loan. if this is the case then loan document will show the son name as co-applicant and so even the repayment is going from father's account and main applicant to the loan is father, the son can claim interest u/s 24.
I really apprecaite Shudhanshu point that a person who does not have any income or did not file any return, can be given home loan by the bank.
so i think that son may have been taken as co-applicant in the case. so son will be entitiled for claiming interest in full.