My mother left the house to three siblings. My brother has lived there for 12 years. They want to sell but 2 sisters say they will charge rent. LEGAL?

The Will should have been submitted to a court for probate (proving), the house sold and the net proceeds split three ways.  In some states, it can still be submitted to pass title.  Without title in the name of the three people to whom it was left, it cannot be sold. The three people can enter into a family settlement agreement, submitted to the court, in which the brother can pay his 12 years of overdue rent (or any other amount) in exchange for the sisters' shares (or part thereof).