You want a design that stays relevant, withstands high turnover, and doesn’t require constant costly updates.7.

As you are finding out, it is so local that the next door building effects your investment. 

Also, you can't know how the cost of materials could fluctuate over your project time, so consider purchasing any materials upfront so you can stick to your budget. 

Selling the PropertyIf your parents decide to sell, they could: Sell As-Is: At a current appraisal of $350k, they could walk away with a sizable profit (after transaction costs like realtor fees, taxes, etc.).

We offered 407 and asked for closing costs.

But for large multi-family, that amount hardly covers your legal fees for one transaction, let alone down payment, due diligence costs, lender fees, other closing costs, etc.

I paid about $1500 in closing costs between title, appraisal, etc, but the original loan was wiped out in favor of a new lower rate. 

Sounds like you need to have a relationship with a couple of good contractors, 40k for vinyl siding sounds high, what was the material cost.  

I am slightly confused about your numbers, though...is the $215/SF the construction cost? 

Multiple people including myself have tried to caution him of the the true costs but he's been repeatedly dismissive and has made it clear we give him motivation and he wants to prove us all wrong (whatever that means).