In many cases the HELOC would make sense because it allows you to hold on to that rate.   

However, this requires careful legal handling.Other options:Reverse Mortgage: If your parents are over 62 and the home is their primary residence, a reverse mortgage might be an option to access equity without monthly payments.Home Equity Loan or HELOC: If you have significant equity, consider a home equity loan or HELOC to cover your parents’ rental expenses, then repay it over time.The Good: Co-ownership can provide financial relief and shared responsibilities.

For example, I have a small HELOC on one property I keep as an emergency reserve and to take advantage of occasional opportunities that pop up.

A HELOC?

We've found the majority of large balance HELOC's or fixed second position mortgages are intended for acquisition or reinvestment towards property that might require new or replacement financing.

@Karolina Powell Have you considered a refi or a HELOC on any of the existing properties that would only take some of your equity and still allow for some cash flow?

I am attracted to the idea of opening a modestly sized HELOC as a "just in case." 

Where I mention the 3-5% delta on a second is that is what it will cost you from a traditional bank (for example a HELOC or 2nd mortgage).

Also, I would also not cross-collateralize the houses if a lender would even do a portfolio loan.On your second question about multifamily, I would not jump to multifamily until you have experienced the common management problems with single-family as the expenses scale with the size of the property as well as the cost of mistakes.I would consider getting Home Equity Lines of Credit (HELOC) on each property.

Cash, developer financing, gaining citizenship, using a margin loan from an investment account or a heloc on your primary in the US, seller financing, etc. are usually the best options as bank financing with attractive rates and terms usually isn't available like we're used to in the US.