Lawyer up and sue, sue , sue. Not only money but your reputation is on the line. You essentially are trying to do the same as the brother has done. Sell somebody else's land. If those sisters tell you to stay off that land and you go back out there you are tresspassing.
Messy family dynamics. It wont be very surprising if it found out the brother and the lawyer are good buddies from way back. It possible you aren't the first person this has happened to with this piece of land.
