I went to school at Ohio State for engineering and have a minor in business and computer science.

Depending on your situation, PMI may be higher and you may have a slightly higher rate. 

It probably helps that I currently have my mortgages through this bank as well because it has had the most competitive interest rates each time I have gone for a loan.

In SFR if prices rise supply drops, high interest rates makes cash flow for new investors go away and supply drops.

I contacted a title company to officially record the sale, but they are requiring 3 separate closings (and tons of extra fees) because there will be 3 liens/private mortgages recorded (one is the original mortgage that I want to reassign since the interest rate was very low; the second will be held by my son to my daughter for his portion of the equity in the home; and the third is the difference which will be between my daughter and my other LLC). 

@Scott AlvarezThere are 3 main parts to a seller financing deal: down payment, interest rate, and price (4th would be the term).

Well you cant BRRRR at 7% interest rate in a market that pays 3% Cap Rate on rentals.  

How are the schools?

But I don't know enough about TX real estate law to determine an alternative that would not require either the due on sale or refi, and I do NOT want to lose this ridiculously low rate.

Also check the fire departments ISO rating.