The Operating Agreement is what will spells out percentage ownership, responsibilities, etc.Are you buying it as an LLC or as individuals?

I assume the lease you have with them spells out where they are and are not welcome? 

I also agree with the others suggestions, make sure your management agreement spells out any limitations on how much they can spend on your behalf and go with that amount as well.

In the case of the condos I bought, the CC&R's spells out how many of the units can be rentals, 21 out of 104 at one.

Your lease should spell out the rules of this exact situation as well, if not, change your lease before you do another one.The way you hold a property is by collecting funds and have an agreement that spells out what those funds are. 

The most important thing is having a legal agreement that protects all parties and spells everything out.

Do you also spell this out very clearly in the listing?

First, I really hate it when people mis-spell judgment as judgement.  

You want to eliminate the "what do we do" questions by having it all spelled out. - Capability and experience of your partner is critical.

Tenant's Right to Break a Rental Lease in Michigan | NoloBeyond that, check the lease that your son signed, it should spell out the process and fee's.