Lots of options here. 

I'm not sure any reputable fencing company would want to put in a fence where neighbors are disputing a boundary line.The other option, of course, is to just get the survey done.

What are my options to cover the $100k difference to still get this house with 0 down?

What are the best options within the city limits as a rental strategy?

Noah, I would call the local officials and ask them for your options.

To me sounds like something an amateur would do who is trying to save a few dollars hiring the cheapest vendor option out there.

.- HELOAN option - There is a small chance that you can pull out the equity using a DSCR HELOAN but make sure to calculate the blended rate and total payment before moving forward and comparing that to a full new 30-year fixed loan.

Find your syndication partners and discuss these options with them. 

At least explain the situation and they'll give you an unbiased, informed answer to let you know what your options are.

When offering a seller options you are selling speed vs convenience, do they want to move on fast?