On this second part, I have done a variety of terms from just offering payments with no interest to adding market interest BUT paying it only once per year on the outstanding balance.

There are so many different ways to make a good living without going down the path of trying to find people to seller finance or doing subleasing, both investment strategies that are full of snakes and usually involve one party taking advantage of another if I am going to be completely honest. 

I'm seeing them at thanksgiving party and I thought I'd use that chance to get to know them.

If you goal is to focus on building your portfolio and you are just trying to offload the burden of property management, I would get referrals from local investors and hire third party property manager that already has the systems in place.

The appraisal fee is a different story as that goes to a third party.

My rental property PM shared the code with a 3rd party local vendor that I am going to hire.I thought someone from my PM company will open door for the contractor but they simply shared the code.

The part I don't understand is why it took 3 months to get rid of them?

They are simply suggesting that they either start to pay up, get a plan to do so, or legally start the eviction process.The "lets find the best way forward that benefits all" angle only works if both parties are interested in doing so.

Are there any park amenities that need ongoing service (pool, laundry, etc)Is there any deferred maintenance (roads, landscaping, pads, pedestals, etc)How are they managing the park currently (3rd party management company, self managed?)

This means that if something ever happened in one of your properties (injury, fire, etc) where the owner could have some liability, having the property owned by an LLC means that the damaged party SHOULD only be able to come after assets in the LLC, and shouldn't be able to come after you personally.