You need to get a standard rental form, and modify it to fit your needs--maybe go to a trailer park and ask to see their space rental/lease forms? Seems more appropriate than a house or apartment form, but look at those, too. Anyways, come up with some specific limitations on what they can and cannot do on your property, and the condition to which you expect it to be returned when they leave. You also need to clearly define any rent payments, late fees, deposits and the terms of cancelation.
Some specifics you need to include is exactly which land they are entitled to use exclusively, which land is not theirs for any use; the farm chores expected of them, and the frequency and quality standards for each chore; require sanitary disposal of human waste at an appropriate RV dump site on an at least weekly basis; water or electrical hookups, if you are providing and, and their costs. Specifically mention that the only usage rights are those specifically granted by the contract or by law. Make sure that what you come up with looks like an official, standard form. (I almost hesitate to say this, but that probably means that they are more likely to sign it without reading and lobbying for additional rights that you do not want to give them.)
Politely tell them that they need to be in their yurt, or at least out of your house by Friday evening. Invite a close friend or relative to come visit for a week--it will give you emotional support as well as their physical presence will provide some intimidation to your tenants.
You need to start looking at them as tenants, not guests, and treat them accordingly.
