Harbor, which premiered at the Westport Country Playhouse last August, is staged by Westport artistic director Mark Lamos. It will continue through Sept. 8.
Beguelin is also the lyricist of Elf and The Wedding Singer. He is collaborating with Alan Menken on the new Broadway production of Aladdin.
The cast features Cummings ("Made In Jersey"), Harrison ("Queer As Folk," Wicked), Stewart (Fiddler on the Roof, The People in the Picture) and original Westport cast member Molnar.
Here's how it's billed: "When fifteen-year-old Lottie and her ne'er-do-well mother Donna drop in unannounced on the beautiful Sag Harbor home of Donna's brother and his new husband, all hell breaks loose. The bonds between kith and kin are tested in this alternately biting and touching comedy about the constantly shifting nature of the meaning of family."