Mostly people with minimal RE experience are adding a single ADU and they often make that choice based on cash flow without taking into account the negative equity position.  

The 1st position loan is paid off but has a second position heloc on the home with 50k balance.

Emphasize that your offer is competitive and you’re ready to move now, or set a reasonable deadline for the offer to ensure the seller knows you’re serious.Use Comparables StrategicallyHave data on hand to support your position.

There are a few programs that can do second position financing but typically underwritten based on your personal income.

The land loan is in 1st position on title which would put the loan to build in 2nd position.

Private Lender Partnership: Partner with a private lender or investor willing to take a second lien position to get you to 85-90% cash out.

Quote from @Michael Challenger: I have no qualms with hard money lending, but I need to learn more about the process and structure to these for typical deals so that I am more comfortable and in a position to reduce my personal risk and risk to investors as much as possible.

Positions with real estate investors or related roles can offer income and experience.

As a sponsor I can't be a member but the reviews I've heard are generally positive.

In my home market of Florida, our insurance rates have made it much harder to have positive cash flow on a CRE deal.