What about just taking a twin size air mattress and using it at POP? I checked on the search engine and lots of people have done it. It's crowded at night but they manage to get the air mattress in by moving the table and chairs when the mattress is on the floor (table and chairs in front of the door or table in front of the window and chairs in the bathroom) and then they prop the mattress up in the bathroom or against the wall during the day. It isn't ideal and it would definitely be "cozy" but it's doable. This way you may only need to pay a small nominal fee for the third adult which I think you have to do at any of the WDW resorts. If you want to have a little more room you could take an air mattress to one of the moderate resorts. Just trying to keep you on site and help you find a workable solution.
My response is a little different from others. Your dad is your dad and you aren't going to change him also you live at home so I can understand your need/desire to respect his wishes. Your BF has traveled with your family before and while this will be close quarters, as you said, you will be out most of the day and your Dad will be at the resort. So, you will have some alone time with your BF. You will be out all day and late into the night having a great time at the parks. I don't think your vacation is ruined and I think you will still have fun. Maybe not as much fun as you originally hoped

but it will still be fun! Wishing you a wonderful stay and the best of luck!