However, since you already filed 2021 and 2022, the adjustment will be happening on your 2023 taxes.

If your plan is to sell/refi before the loan hits it's adjustment period, this seems like a no brainer (assuming there are no pre payment penalties). 

HELOC is an interest only payment, an adjustable rate, and you can draw funds up and down from $0 to your total line amount.

New construction will not be the identical house since everything in the house would be new and the house would be built to modern building codes.

Is it an adjustable rate?

If you can swing it, I would tell her that you are going to have to adjust the rents to the market level, and give her as much time as you are reasonably able, maybe 3 to 6 months to vacate, provided she's paying.

The cost basis rarely stays the same over time, and once it’s changed, it becomes the adjusted basis.

In this business no two investors can accurately compare cash flow unless they use identical systems for calculation and even then the number is only realistic in their own minds.

Identifying a d purchasing properties that are undervalued due to under market rents caused by owners with a lower purchase basis that are terrified of losing tenants and raising rents, will definitely provide you with immediate upside appreciation when adjusting rents to market rates as well as covering all your holding costs and a cash flow reward every month. 

It seems like you've correctly adjusted the carryover losses on Form 8582 to reflect the net income for each property.