FFL is a good bank.

Also, call the note holder every year and offer 57% of face value for all cash right then.

For example, if I buy a duplex for $100k cash, spend $40k on remodel, I then go file a lien against the property for $140k (my private lender is the lien holder).

The atty or title company cuts checks to the lien-holders and could be a long closing depending on what.  

Your credit will be ruined if the ex decides to stop or simply can’t pay the mortgage and the mortgage holder isn’t going to care that the ex was suppose to be paying it.

Subject to, where you essentially take over the payments for the current note holder?

Agreed, if there is no estate (relative/heir) to fight the foreclosure or the estate just let it go then the bank as the lien holder will foreclose and auction it. 

I didn't see any info in the file at all from the first lien holder, so I'm not sure what the status is with them.

It as originally for Rental Property Owners, but there you'll find wholesalers, buy and holders, etc.

If you go a non-bank route perhaps they won't look at your personal credit, hard to tell.Transferring from an individual to an LLC won't NECESSARILY trigger the due on sale clause but I would probably inform my mortgage holder before taking those actions.