All hail Christine Ebersole; all hail Mary Louise Wilson.  Show stoppers of the first rank in this musical, detailing the slide of the Beale mother and daughter (relatives of Jackie Kennedy) into a life of shared decreptitude.  The Grey Gardens of the title is the 28-room mansion they inhabit.  Forget the weak book, or the illogic abounding; when Ebersole [shown] starts to sing, you're transported to a time when "character and a clarion purity of performance came first." [Walter Kerr]