Look for Birth Registration of William Gregory. Yes, there is a christening record dated 12 Dec 1784 at St. Dunstan and All Saints, Stepney, Middlesex, for William Gregory, 22 days old, son of John Gregory, Occ: Shipwright, and wife Elizabeth Gregory. Hmmm. The Seabrooks were Shipwrights and their children were baptized at St. Dunstan and All Saints in Stepney.
Elizabeth married John Gregory.