Why wouldn't the owner just push back the close date or let you know they would be there when you took possession and then move out in a month? 

You should complete the eviction process to be entirely sure you regain possession legally.

Especially when that person has your high value asset in their possession, tying up cash, or potentially neglecting, or even harming the asset.  

This is in North Carolina, if it matters.If tenants turned keys over and signed a document stating that they have vacated the property and returned possession to the Landlord, are we under any obligation to keep the possessions (mostly random trash/small pieces of furniture/paintings/food/etc., likely less than $100-200 of value total) for a set period of time, or can we simply dispose/donate as needed?

Don't require it but clearly state in lease that you are not liable for renters possessions and recommend renter insurance.

You may end up having to evict him to regain possession of the property.

I actually think it would not be more than a few hundred, not so bad considering the monthly rent is $3200, and I could in theory charge it against the security deposit or directly to the tenants (at least I think so).I am thinking that I should allow the 4 months to finish, get the tenants moved out, regain possession of the property, and then if necessary due to needed repairs let on that I knew about the 6th tenant, as a point of leverage.

The two bay area properties will help you gain financial independence quicker while in your possession that if you sell them now to buy anything in Tennessee. 

Does anyone know if I can add a term to the agreement, to have tenant responsible for pest control after certanly weeks of taking possession of property?

That's for possession of the property.