Tenants are fine with the cameras.

I need to install cameras that record good sharp video at each exterior door of my triplex. 

What I would like to do is to install a security camera/floodlight combo (like a ring camera) for my renters to use.

If you do not want to talk to a camera you can make a slide video (example of a $5 slide video in my signature line) Video's are cheap, last forever, and can be found by people searching for you services.

I am currently a freelance camera operator and photographer, but my goal is to be a full time real estate investor within the next two years.

Does anyone have any recommendation for a camera system that would alert us when someone enters a property?

Yes. wireless Reolink cameras with the solar.

You won't know where exactly until you open up the wall unless by chance you or a good friend of yours has a good infrared camera that can help you see what is going on.

i agree with you David, i watched an episode yesterday of Flipping Vegas, where a boa constrictor holds up reno, its obviously a pet, and the scene where two workers evacuate looks completely staged, not to mention, the camera man and camera watches the snake approach the house, then stays in the house and gets incredibly close to it?

This will help the landlord in proving damages to the property later on.13) surveillance camera - for multi family homes or large properties, the tenant should acknowledge on the lease agreement that he is fully aware that the ppty's common areas is under camera surveillance and will not consider this as invasion of privacy.14) proof of funds - this will not be on the lease agreement, but I would ask for proof of funds to be submitted along with the application form.