Leveraging Equity from Parents Real Estate Portfolio

Hi BP Friends! 

I am a long time listener but this is my first post! My parents have a small portfolio of single family homes that have all been paid off this past year leaving them with about a 1.5 million in equity and have HELOC's are in place on a few of those properties.

How can I leverage their equity when I find my next BRRRR property? Will I want to list them as co-owners on the title? Can they borrow the necessary funds from their HELOC and I create a note? Are there other private money or creative financing strategies I am missing?

Thanks in advance for the feedback!