Two bishops usually cannot beat a rook if the rook's king stays active and the rook checks from a distance. The danger is a king driven into a corner where the bishops mate with their king's help.
Two bishops against a rook is the most dangerous of the rook-versus-two-minors endings for the rook's side: the bishops control both colours and can build mating nets in the corners. Nevertheless it is a draw with correct defence, and this position is a model.