It would be in the interest of all concerned to find a way to resolve this. Ideally, you would buy out their interest with some credit given for the advances you have made.
If a resolution is not reached and you do not agree to sell, then they can bring an action for partition, which is literally dividing the property in an equitable manner. In this case, with a farm, that may be feasible. One party may get the portion with buildings, but a smaller portion of the land. The determination of a fair division, however, can be costly with each party hiring attorneys, appraisers, etc. If the property is not feasible of division (which would typically be the case with a city home, for example), then the property would be ordered sold and the proceeds divided.
