Constance Bennett was a very sophisticated, versatile performer. She managed to steal Two Faced Woman from Greta Garbo, which was no small achievement. She returned to films after a long absence to play Lana Turner's mother in law in a remake of Madame X.
No brother but Joan and Constance did have a sister named Barbara, who was briefly an actress. Barbara's son was Morton Downey, Jr., who was kind of the Jerry Springer of the time.