Clubbing and gift

Father invested in ppf of son and daughter. ppf have matured and got credited in Son and daughter saving account. So this is a case of gift from father.( correct me if wrong ) .. Son and daughter give the amounts as loan to third party and earn interest thereon. Father has to paid interest on educational loan of son. So question is whether son and daughter should transfer the interest amounts to father account ( in the form of loan or gift ) or any other way if you can suggest it would be great help.