Once purchased and repaired (with a HML) we refinance with a long term loan or a DSCR loan and obtain quite decent cashflow while enjoying the appreciation Denver offers.

Houses are designed/built as rental hardened so minimal repair/maintencance for at least 15 years.

"I made $3000 off rental property A last year if you don't count repairs or capex!" 

You need a bucket of cash for reserves, emergency repairs, or leverage to find/buy/create a good deal.

The after-repair value (ARV) is projected at $428,000, potentially reaching $477,000 if sold individually.Two houses require rehab, while two are rental-ready.

What would be the return on the investment of the repairs?

The buyer transfers the property over to their name but keeps the mortgage in the name of the seller, continues to make the payments, takes on full responsibility of the property, all repairs, maintenance, etc.. 

Inspect for any rot or damage periodically, and replace or repair sections as needed to maintain its condition.Potential Upgrades / Considerations: Security:Enhance security with robust locks, a video doorbell, and exterior lighting.

There are some people "real estate consultants" who will give you detailed reports: if they think this is better for a flip, rental, what rents you could get, recommended repairs (not as detailed as an inspection report). 

Less how much repair is needed?