Granted we only have 17 but still, I’ve never used anything except a simple excel spreadsheet and all my rental properties have a separate savings account under my main account at my local bank.

Total profit less closing costs and commissions will be about 42,500 each or 85k total.I would for sure get a construction loan, may be worth approaching 2 or 3 different banks and getting separate construction loans from different banks. 

For California, here are a couple of options:California Vacation Rental InsuranceUnmatched Short-Term Rental Insurance for California Hosts 

There may be something called a "Due On Sale" clause.Check and see if all tax parcels are included in one mortgage or if they have separate mortgages.You have to have him spell out what he considers to be a "partial seller financing".

At its most simple we’re separating the appreciation/capital buildup benefit from the cash flow benefit.  

Mitch Stephen out of San Antonio has had 4 called due in the last couple of months.

***depending on how far the house is from the coast, you mayalso be required to have a separate Wind or Hurricane deductible.

I think if you are going to keep all three parties involved as owners of the deal long term then you need to separate yourself as a renter and a contractor.

Should be ok for couples.

Mom’s estate plan should probably address this separately from you.