Neither owner can be forced to buy out the other; a buy-out is voluntary (like choosing to buy anything is voluntary). If the two owners of property cannot agree as to what to do with the property, one of them can bring a legal action (traditionally called an action for "partition," though your state may have a different name for it) in which the court is asked to order that the property be put up for sale. The court can order that the property be listed for sale and that the proceeds of the sale (after paying costs of court and sale, and paying any mortgage) be divided among the owners.