Money today is worth MORE than money in the future.

The reason I want to do this is so that the ADU is worth more on an appraisal.

It's possible, but seems worth the risk. 

Is it worth keeping the house and increasing the rent to $1750 or should I sell in the market that we are in?

While they do eat into rental margins the larger profit came from the sale and the added rental profit was not worth the hassle of being a landlord.

He has bought and sold over 300 million dollars worth of real este and doesn’t care that he’s going to lose some money by almost giving me this property.

These can be fairly automated for you as well to help save you 10% which on 2 units could be well worth it. 

I think it's worth it.

The property is worth 800k.

In general, if there's nothing in zoning or the deed restrictions prohibiting the division of the property, it's mostly just getting it resurveyed and presenting the new subdivisions to the local government (county usually) to have each lot recorded as separate parcels.