I am hoping to roll these two into one loan and reduce my monthly payment/ interest rate on the HELOC as I will be having the debt long term.I also currently own a 11 spot RV Park which I own all 11 units and is currently generating $10,375/month in rent.

They’ll take the design plans and generate them easily. 

The strategy involves using the HELOC for a flip to generate fast cash, reinvesting profits into long-term rentals, or exploring alternative ventures like short-term rentals or partnerships.

@Eugene Lubman Selling the property to your parents allows them to generate passive income while enabling you to perform a 1031 exchange to defer capital gains taxes.

The problem is the HOA doesn't allow VRBO rentals, only year long leases so I wasn't able to generate cash with this property.

While an SDIRA will have UBIT on leveraged real estate, a solo 401k is exempt from UDFI (unrelated debt finance income) generated UBIT.

There are a ton of illegal basement apartments all around Hudson County--maybe 10-15 years ago there was a program (at least in Union City) where many of these apartments were made legal, I think partly as a way for the city to generate revenue, and partly as a way for the city to have some oversight, since people were renting these apartments out regardless of their legality. 

If their credit history is sufficiently long to generate a reasonable score for them then the credit score tells you the answer! 

When I refer to the MLS, I'm referring to the real estate agent generated list.

It is very unlikely that all my properties will stop generating revenue at the same time.