It sure makes sense  - the builder has no skin in the game in controlling costs whatsoever.

Do you have any control over what the existing owner can do to the property?

If you can't keep control of your personal finances, you are highly unlikely to succeed in real estate investing.

If you can buy within a 2 hour drive (maybe Sacramento area, which is what I'm considering), you have a lot more control as far as checking on the property than buying OOS. 

Pay it off with a commercial DSCR refinance loan once you've gotten the rents up to an amount that will allow you to cash out on your HELOC.I like using my HELOC but only in short-term scenarios because it's a floating rate and I can't control when or how the bank will make adjustments to the payback variables. 

Because I don't control the process.

Also you may want to consider Checkbook IRA (aka IRA owned LLC), which will enable you to bypass the custodian and have checkbook control over your retirement funds.

I wouldn't look at fix and flip for 100+ year old properties I'd recommend urban infill new construction much more control less stressful more advanced more value easier exit, etc etc 

A very big reason for this, I know my target market's with pin-point precision. 

Either way, I recommend finding peace with what you can't control (whether that is eviction or them living in the mobile home); otherwise, you let the siblings keep winning if they impact your happiness.