So, you're actually making the argument *against* debt (not for it).I think you mis-understand debt, risk and the alternatives.

That said, I'm grateful for the alternatives you present--you're keeping the bottom line in mind, so I appreciate your help in exploring options that achieve the bottom line for the investors. 

Or of any alternative strategies to make this work?

I’m also open to alternative strategies, such as private lending or passive investments in funds, to diversify and balance risk.Does this phased approach seem reasonable given the higher HELOC rate?

Alternatively, yes you could sell, pay taxes on the gain, and use the proceeds to help your mom directly.Would suggest for you to talk to a CPA and a 1031 specialist to confirm your best move!

(Not judging the merits of the deal, alternatives, etc...)

Perhaps do a case study with a hypothetical deal you think is typical for what you are looking at and compare it to the alternative investments you might use and their expected returns.

@Tina Artigliere@Alicia ProkosFor these Quest Solo 401k plan account holders, what is essential is to find a new Solo 401k plan provider who offers a Solo 401k plan with the service and features that the account holder needs such as Solo 401k loans, alternative investments, Roth and Mega Backdoor Roth Solo 401k contributions, 5500-EZ & 1099-R preparation and filing, etc.The process entails restating the Quest Solo 401k plan where the Quest Solo 401k plan documents are replaced with the Solo 401k plan documents of the new Solo 401k provider. 

or alternative lenders?

Unfortunately, some renters will say anything—even things that make no sense in an alternate universe—to avoid responsibility or financial consequences.