What are the steps to making this as easy and secure as possible? 

Keep in mind, it's s security deposit, not the rent for the last month of the lease.

Bottom line is it's better to cut your losses and move on.You can deduct the cost for pest control from the security deposit because that is clearly damage caused by the tenant.

I pay for this service at no additional cost to my buyers.The option can not be exercised if an eviction takes place per my "breach of contract" clause which states:If the Tenant/Buyer shall fail to keep and perform any of the covenants, agreements, or provisions of this Lease/Option, or If the Tenant/Buyer shall abandon the property; it shall be lawful for the Landlord/Seller to repossess, and enjoy the same as if this Lease/Option had not been made, and thereupon this Lease/Option and everything herein contained on the part of the Landlord/Seller to be done and performed shall cease, determine and be utterly void.The tenant/buyer is clear about their maintenance responsibility as future owners of the property per the clause in the lease that states:The Tenant/Buyer accepts the property “as is" on the date of execution of this Lease/Option The Tenant/Buyer shall henceforth be responsible for all maintenance and repair upon said property, both interior and exterior.

@Leo B. Reach

Isn't that a breach of contract since he didn't pay the mortgage in 2 months? 

I kind of doubt they will be unable to secure insurance or financing, but it's definitely worth investigating the potential implications before laying cash on the table (or lock it in with a due diligence contingency for this matter). 

Annette in my opinion it boils down to security and risk and your comfort level in those two areas. 

I have to maintain security practices.  

I'm considering a rental agreement that states the move-out date in the contract (with option to extend under certain terms), and has them pay the full 2-3 months' rent up front, with a half-month security deposit also due prior to taking residence.