If I recall correctly, there is a second loan on this TS. Either on a credit card, or from a mortgage lender. So even IF (unlikely) the developer consents to accept a deedback in lieu of foreclosure, the outstanding loan remains. The OP would have to either pay that off separately, or convince the developer to refund what they accepted from that lender (even more unlikely).
I really don't see an alternative to paying off the total, as agreed, and count it as an $8900 lesson in how the world works.
All in all, it's not the world's end. His/her family will hopefully get some great memories after the bad taste of getting taken for a ride financially fades. The reasons the OP saw for buying this vacation resort are still valid.
We wish you well. Stick around TUG. Learn to get the most from it. Enjoy some great vacations.
Jim