All too typical park owner who took all the profit out of the park without reinvesting in the business then wants to sell you the potential he was too cheap to invest in. 

Many lenders won't allow you to sell or refinance the properties individually if you have these on a blanket mortgage.

Depending on comfort and cash, it might be a viable option as you can build equity and then sell without having capital gains, assuming it's your primary residence and you've lived there for 2 years.

Fake investors, you can sell the dream, the hustle is sold separately  thats why lottery tickets sell so well.. dream with no effort. 

@Ilia Zakharav, There's no problem in selling individual units and 1031 exchanging them as individuals. 

There’s no reason to go through a disaster (I'm mid recovery myself) and not get the financial upside by becoming the developer and selling a finished product versus raw land.If you have to completely rebuild, it’s a two year process at minimum.

Multiple places, then you start reaching commercial territory when you sell and try to move it all as a business.

Question: why would one choose to build an ADU when existing structures sell for less than the cost of development?

If you do have to move because of a job, you would be safest (in my opinion, i am not giving legal advice or financial advice), i would sell that property to ensure that you did not just purchase with the goal of moving out early and taking advantage of lower rates and lower down payments for purchasing your home as a primary residence. 

That way when a deal is brought to you, you know the seller actually wants to sell.