Hi Sadie. Is it possible to refinance a private/seller-financed mortgage into an owner-occupied FHA mortgage? It sounds like your goal is to use your HELOC's short-term but to not be stuck with those monthly payments into the indefinite future. I'd recommend finding a property that the BRRRR method will work on where you'll obtain enough funds in a cash-out refinance into an FHA mortgage to pay off the HELOC's that you used for part of the purchase and the assumed renovations. You can use a private/seller-financed mortgage to purchase your next property.
I'm doing this right now on the four-family at 45-51 Aldrich Ave. Purchased for $195,000 in May 2021 and used a hard money lender to finance $152,000 of the purchase. Spent $20,000 in renovations and will be closing on the cash-out refinance at the end of this month (6 months since purchase). Used cash for the down payment and renovations but could've used a HELOC to achieve the same results.
Appraised value is $265,000 and getting a 30 year fixed mortgage at 3.875% for $185,500. It's not a perfect BRRRR where I'll get all of my down payment and renovation funds back but it's pretty close!