Generally, interacting with these warriors are just lawsuits waiting to happen.   

The first pillar is avoiding unnecessary and risky activities (don't drink and drive, insurance generally won’t cover your poor decisions) and take good care of your investments - these simple steps will help you prevent lawsuits before they even occur.

I got a letter and phonecall from there attorney and they will be filing a lawsuit against me.

If your business gets into a lawsuit and then they can prove that you commingled funds then they can pursue your business assets and also your personal assets.

The majority of single family homes with mother-in-law suites or ADU's.

You say you put language into the PA that said "tenants are to remain month to month leases" and this was fully agreed too by both parties then you have a nice little law suit on your hands. 

The agent is who one would contact for lawsuits and other related issues. 

Because most landlords don’t follow all the legal requirements to maintain their LLC as a separate entity.So, what else can a landlord do to protect their personal assets from a business lawsuit?

It separates the property from you personal assets (like your home, car etc) thus limiting your liability in the event of a lawsuit. 

They've got so many lawsuits they got to deal with, it's no wonder he doesn't have time to run his company anymore.