Hi, Julieanne! Happy Birthday! Disney is a great place to celebrate such a special birthday!
The least expensive way to go would be to book 2 rooms at a Value Resort. Each room can accommodate up to 4 guests. It will be tight, but I am guessing most of your time will be spent out of the room celebrating, so I don't think you will mind! Keep checking
HERE for special offers that might be available during your stay. Hopefully you will be able to save some money.
By staying on site, you will not have to worry about airport transportation, transportation to the theme parks, and you can also take advantage of Extra Magic Hours.
Wishing you a very magical birthday! Have a wonderful time celebrating with your friends.