Ask them if they're okay with the smell of the orange natural cleaner (odds are these guys will also be afraid of chemicals). 

If you are in an area of harsh, cold , winter months make sure the end of your lease does not happen at the same time.It will be very hard to rent.So If you didn't like them and the lease was set to expire at an off peak market leasing time you might want to get rid of them now.

It may seem harsh, but put it in the lease that the tenant is responsible to call a locksmith at their expense. 

Sorry, not meaning to be harsh.

We were successful with a new chemical treatment. 

***(This may seem unusually harsh or strict.

Things like old ovens, random chemical waste, excess trash left behind by a tenant, etc.I used to drive a sedan and I was able to make that work, but having a truck is just a bit easier, in my opinion.

We hired a pest company that used a new chemical treatment at the time, which would have been about 2013. 

The prognosis from the cleaning crew was that the chemicals they would need to use to clean it, probably wouldn't make it very safe as a fridge for food afterwards.

Not to be overly harsh, but sounds like it may be wise to work on your personal finances before investing in Real Estate.