Rebuilding costs doubled overnight (ask me how I know). 

@Dustin Verley, They will be spending 40 mil to rebuild the existing station into a new state of the art one.

Because of all this, I am going to sit back a bit and just let things settle to rebuild my reserves and investment capital.

Investors will take advantage of this situation by making quick, cash or pre-approved financing offers to help get the family some much-needed funds to help rebuild their lives, and the investor gets a fixer-upper for below market value. 

What I don't want to see is the throwing of good $ after bad AND the upside of selling at a loss now is that we will know what the loss is and can start the "rebuilding" immediately or whenever they feel up to it.

We have a fair amount of relevant experience including many rehabs (over a dozen) and right now are rebuilding two heavily fire damaged units (over $200k damage), but no ADUs.    

Ours is completely custom... knocking down our garage and rebuilding a 1,030 footprint structure (2,060 total sq ft).

The tenant (me) can buy a policy which covers the landlord's building, enough to rebuild it from the ground up.

I would break down your strategy to the nuts and bolts and rebuild.

You also need to have the rebuilding costs (Building Replacement cost) updated to include the changes to the basement.