This sounds a bit complicated.  But I think that the documents that are in question needed to be reviewed by an attorney.  If you "sold" the proeprty or rented it with an option to purchase and the buyer backed out, then he is in breach and the damages are those permitted under the contract or under your state laws.  Now, if he remains on the proeprty as a squatter you may have to evict him if trespass will not allow you relief.  Please get help.  Don't just go on the property.  It is unclear what the 60 days is here without reading the agreement.  Good luck.