I am in the beginning process of getting pre-approved for a HELOC.

I am in the process of buying a rental property, and have taken out a HELOC on one of my existing rentals to use as the down payment for another.

The long term plan is to HELOC the property when we are finished and use that as a fund to BRRRR other properties.

@Tyrell D BradshawIts the basis of the BRRRR investment strategy, For exampleAfter you purchase and rehab a property and  you have 100,000 in Equity in a property, you then get a loan on that equity, a HELOC usually for 75% of that equity.

I opened a HELOC on this equity which has given me flexibility on other deals.We lived there well for about 3 years.Now it is rented for a solid 1450/month.

I used a HELOC for the down payment and my cash for the rehab, although I could have done it all on the HELOC in hindsight.

Also HML is still a loan that needs to be approved, and it can still fall through for various reasons.Also if I used a line of credit, I would do it as a HELOC, so the rates would be at least half of what you mentioned.  15% is pretty high.  5-6% can certainly be achieved.

To get the most out of what I have would it be smarter to pay off the property and get a HELOC on the whole worth of the property or should I just keep the cash that I have  and get a HELOC on the current equity that I have on my property. 

Other funding options could include creating some kind of a partnership with the family where they let you handle the rental, and you pay them in monthly or quarterly installment payments (seller financing), hard money (doesn't sound like the smartest move for this property), or potentially taking out a HELOC on your current mortgage depending on how much equity you have in that property (but still probably not enough to buy out the family).

A HELOC can be used as a down payment, but not as reserves.