In regards to the comment expressed a couple of times that all parties must agree to sell, I doubt this is the case. I suspect you could sue and force liquidation of the property .Again as I mentioned this may vary from state to state and should be addressed by attorney. Let us know how it goes.
An attorney is needed in this situation. All persons on the deed to the house need to come to a meeting of the minds.
After you settle the issue and if everyone agrees to sell, feel free to contact me as I would like to assist.