My main concerns are demand for “duplex style” (will this be always 2nd rate demand due to the connectedness?)

The area that I live in is more of a long term appreciation style of investing since the price of houses vs the rent you can receive isn't that great.

Specifically for SFH and MFH that fit the more BRRRR styled model. 

If your tenant is leaving soon and you’re just looking to replace them with a new tenant, and you really can’t wait for them to leave before starting to show the unit, then I would coordinate a few time windows with the tenant when you can host open house-style showings.

The material price is very low since its out of style, but its clean and will last for decades in a bathroom and kitchen.

There are so many different styles and techniques to investing in real estate, and they all work.

Your part of the deal is to manage the rental and ensure your parents maintain their bill free life style.

Construction is reimbursement style, so you will need to have at least 10-15% in reserves set aside to start the project.

I would be interested in reviewing your comps on how you determined your ARV.Closings prior to your purchase (Jan 2022) in the immediate area for similar aged homes/style etc. were12/21/2021 - $355,000 for 1.300 sf– 4 Bed, 3 Bath (Converted Garage Space)11/29/2021 - $310,000 for 1,309 sf – 3 Bed, 2 Bath12/3/2021 - $285,000 for 1,125 sf – 3 Bed, 1 Bath11/10/2021 - $270,000 for 1,125 sf 3 Bed, 1 BathDid you heavily weigh value for the unfinished basement in your ARV?

Your first step should be to talk with the Placer County Environmental Health Dept regarding the availability of a large septic system on your lot.