i would do some thinking and discussing and maybe talk to some professionals before you just tossed that much liquid cash against a perfectly decent mortgage... especially with college expenses coming up!  

Then, liquidate to pivot to debt investing to generate cash.Here is one thread I've just posted some about (cont reading down):  https://www.biggerpockets.com/forums/48/topics/1170072-what-...I'll keep just this short as maybe this isn't what you were asking for in your OP.

These loans generally carry a higher interest rate than first-position mortgages because they are more risky for the lender in the event of a default since they are the second party to get paid in the event of a liquidation. 

Check if their liquidity and net worth is a cash position or mostly retiree funds you can't touch.

I'm not sure it would work in the way you're thinking in the mainland because lending/liquidity is difficult here in this current market.

Helocs must also be calculated in underwriting based on fully exhausted payment meaning even if you only use a portion during the next purchase they underwriter will hit you with the full payment for risk.Cash out on the other hand is a liquid reserve tax free and it only requires (1) mortgage/lien.

If you have liquid reserves - say $10k +, and IF the property is in good, not average, not fair, but GOOD condition, and the property is not in a “war zone” and not in a declining area, and the property is not in a city where it is or can be subject to rent control, then you might have negotiated the deal most investors strive for but seldom achieve. 

Are you planning to flip and build up more liquidity?

Listing agent was amazing when we were ready to liquidate.

Do  you have $20k liquid or invested on something?