These clowns are hilarious. Others have already mentioned the correct course to take. Cut off their food and water and wait for them to wimp out. Maybe we'll even get to see them crying on TV about being tortured by Obama or whatever.
They're in an unused building in the middle of nowhere hurting nobody and threatening nobody. What they want more than anything is for the authorities to swoop in and thus validate their position and give them an excuse to escalate. Don't play into their hands. Just cut them off from their Coors Light for a while and they'll give. We can always arrest and charge them later on.
This is like a late christmas gift.