Does that mean there is a barn or isn't one? Where would you store feed and supplies out there? You should go out there and take pictures. How far is it? Would you eventually move there for the short term too, or just keep horses there...
Is your BIL a horseman with skills already or is he new to it?
I'd definately put up hot wire to start, and over time replace the barbed wire with more hot wire and/or field fence of some kind... and use the heavy gauge stuff too.
There isn't a barn but a barn near that I can temp use to store feed if I need to. It's several hours away. It would be weekend commuting for now which is what we had decided on since we couldn't find anything around here. It's very pretty and isolated. If we don't eventually move there which is probably what will happen it will still be ok. My payments are lower than my boarder fee and everytime we go up there we drop 100 dollars on motels anyway so now we will just stay in the 5th wheel. We have 14 acres with access to another 20 of pasture.