There is a formal agreement, "Co-Lisiting" agreement or "Cooperating Broker/Agent" agreement.

When tenants choose to 'not behave' according to their contract, you should always try to remedy the situation by holding them accountable and then, if the still choose not to cooperate, find a creative way to 'encourage' them to move out and leave the house in good condition, without putting yourself at the mercy of judges and lawyers. 

If the other guy has equitable interest and wants to prove it he will get back in touch with you or cloud the title.As for the lockbox, if the guy won't take it off I'd tell the seller that her property is not secure as his box is there and he is not cooperating and could have copies or could give anyone the code.Tell her that she should call a local locksmith and get them to pick the lock and put new ones on.

Keeping the door open to terminate is a good practice in gaining cooperation, even if you don't intend to terminate (and they'd be in there too, so you may have an eviction).

If they are completely not cooperating and are damaging the property then eviction is the best option.  

@Jessica Cooper I realize that after a situation like this occurs it is natural to look for someone to blame.

Just cooperation that helps you get more deals done with better contracts.

Let's keep in touch and see how we might be able to work in cooperation.

If the tenancy is worth saving and the tenant is cooperative, then we will make the repairs or replace the components as the need occurs.We haven't had a situation where we did not repair/replace a required appliance.

I'm wondering if I'm going to have problems with these tenants cooperating and three of them are still in a lease until the Sept of this year.