版主不在，我试回答

First of all, assume: John and Beth are a couple. The HELOC is a loan under their primary home.
1. LLC is an entity - even they own the company 100%. Try to make a clear line between LLC and their family asses.
2. The LLC should have a doc to borrow the fund from the private fund (their HELOC fund) and agree to pay back the interest and principle monthly.
3. In this case, it will be easier for LLC's tax issue, and their personal tax (you may ask CPA for this part).