Mortgage Loan Scenario and Innovative strategies for HELOC use

Hello,

I have two separate scenarios regarding lending so I will break it down.

First, I own a primary residence in (bay area) peninsula that my mother currently lives in and I recently took out a HELOC. I live with my partner and two kids, and we are planning to purchase a new home within 6 months in the following cities: Lathrop, San Jose, Morgan Hill, and possibly Fremont. My partner suggest that I sell my primary and look for a 1 bedroom apartment for my mother so we can use the proceeds from the sell to buy our new home. I rather keep the primary and find alternative options instead. One thought is we could use the HELOC as a down-payment and apply for loan together. However, does it make sense for me to be a co-borrower since my DTI is likely higher based on primary mortgage, credit card debt, car note and now a HELOC (that has not been used)? My partner is a Branch Manager at a Bank, and I'm sure she'd have no issues getting approved as a single borrower based on her income, DTI and savings. (Thoughts, suggestions)

Second idea:
Use the HELOC for buy and hold REI out of state. It would be challenging to buy something in the bay area that cash-flows. I could leverage the HELOC as a down-payment/closing costs and be able to invest in multiple properties. (Thoughts suggestions)

Thank you,

Armand