My main concern is monitoring the exterior property while the property is vacant.

Although I understand kids are hard to monitor all the time!!!  

Put in the letter that pets will now be monitored and if it continues it is a direct violation in the lease and grounds for eviction .

You could offer equipment & monitoring for maybe $50 /month or sell them the gear and then move the system to their next home. 

We also require and monitor minimum insurance levels for tenants occupying our properties.

There's usually some good locals who monitor those forums and I think they might be able to point you in a good direction for a local lender. 

Put up some cameras around the property, an automatic light by the main door, a sign on the lawn that states the property is under surveillance and is being monitored. 

If half of the homes have been renovated, I'd closely monitor those expenses and confirm them.

We are in a mindset to constantly reduce expenses which is an important aspect to monitor, but do not compromise the service providers who perform well for you even if they are a little higher in price than a general handyman.

., as ours is also required to be monitored (by 1st Responders) 24/7.