Keep in mind there are 8,000 different lenders in the US...so, obviously we cannot speak for all of them...but the absolute best of the best lenders in this space, that have the most aggressive pricing, won't penalize you with 2 points for one option over the other.I would also question that IRS definition - that is not the case.  

There are so many caveats and unknowns here that this is just an attempt at an idea...Option 1, the four grandchildren living in the property buy out the other two:-Estimate your PITI payments based on the expected payout to the 2 grandchildren being bought out.

Solar energy is becoming a more popular option for homeowners, but it can be a costly investment that won't pay off when you come to sell.

Someone mentioned Quickbooks, also another good option.

I've never had any issue or problems with wholesaling or assignments or options or double closes, all of which I've done.  

The sellers don’t want to return the earnest money, creating more problems.If anyone has experience with this, could you advise on legal options?

Yes the interest rate is higher but it gives you optionality, in case your extra money for helping pay the 15 yr note disappears or your investment goals or priorities change for that money.

Another option if you both have self-directed IRAs is partnering them together. 

Other options?

I would highly consider house hacking if that's an option for you.