I'm thinking of installing a security camera. 

These are highly configurable and have the ability to set a temp range and lock it out so that it can't go above or below a max.I have a digital watchdog commercial grade camera system.

Ie commercial sink, appliances, cubby’s, cabinets, security cameras, park outside, and is contemplating taking the toilets from the two new bathrooms she had installed and the water fountains.

We had to install a camera to hold them accountable to clean up their dishes. 

I moved into a building about 6 months ago, They said it would be secured with cameras, secure entrance and all..There is one camera in the main entrance of the building but it has been smashed or ripped off the wall (gone)....

From the guy screaming at the workers to the workers being subject to the screaming, both are indirectly accepting "their roles" and stretching the amount of craziness they can put up with.Consider this, for most people television is a powerful idea, just grab a camera, get as few friends as "crew" and you will se how people change their behavior, for good or for worst.

I am debating installing security cameras on my triplex, but am concerned about legal issues.

Do not include travel expenses, extra hotel rooms, etc for your children, your children's nanny or other relatives, unless they are also involved in your real estate decision making.  

If you do the video, have all parties who are present state their name, date and the property address on camera.

Anyone goes to a window or drive-through with a deposit slip, they are going to be on camera.