You can only reserve one room per AP holder now - Disney changed that earlier this year. There were several posts from people who weren't very happy about this change.
If you are treating another family member to a trip, you would be booking the room and paying for it, but the names listed on the room would be the guests you are booking it for. You can book as many rooms as you like, so long as the guests listed for each room are different (think Magical Gatherings type reservations). But you can't do it with discount codes unless you follow the rules (i.e., if you book three AP rooms, there needs to be one adult AP holder booked in each room).