You can book an extra seat for father or self or whomever, but the extra seat must be booked with name of person who will benefit from the space. The idea is that the extra seat is kept next to that passenger, not randomly assigned somewhere on the aircraft. So if you want father to benefit from the extra seat, it must be booked in his name and associated with his ticket, not yours.

BTW, DL doesn't give FF credit for extra seats.