And as long as the amount you are using for investment meets your reinvestment target then you could live in one of the units as your primary for a while or forever.When you sell your current primary the 170K of profit will be tax- free. 

A good solid profit but not enough to justify 20 months of work.

The biggest challenge I can see for this is that I hear it's a pain in the *** for the seller to go through a local community bank and confirm their income for their approval for a mortgage, and there are local/community banks that will approve 95-100% LTV loans based on how profitable the deal is.

To start, I’d like to ask you a question: What is more important, purchasing real estate where you can obtain 100% return of your capital through the BRRRR investment method but otherwise break even or even worse lose money or alternatively  leave some of your capital in the deal but earn a profit when the property is sold? 

To do it profitably?

This could range based on how much risk and work you're taking on versus their financial input.The key is to be clear and transparent about expectations, like how profits will be split and who is responsible for what.

Look to see if they are growing and profitable. 

Since Nassau County home prices are high, ensuring there’s enough room for profit after the flip is essential, especially considering the potential family dynamics and the costs involved.It’s definitely doable, but being upfront with the family and working with an estate attorney are key to making this work for everyone.

Thus, the "Other Costs" increase significantly if a person were to sell their property in the chosen year.Just fill in everything, including the Advanced Inputs (you'll need to change default 30 year mortgage term to 180 months for your 15 year mortgage)Transfer costs will depend on your state and local municipality.Tax on rental profit will be your current or projected personal tax rate.THIS CALCULATOR IS PRETTY THOROUGH! 

You could use the monthly profits to pay down your heloc which at current pace would take about 8 years or so.