Hi Barbara
I found the following in the 1851 census:
William Joy  Head   M   53   Plumber   K.Brenchley
Ann Joy       Wife    M   54                   K.Maidstone
William         Son    U   21                   K.Tonbridge
Elizabeth     Daug  U   23                   K.Tonbridge
Frederick      Son    U   18                  K.Tonbridge
All living at Priory Terrace, (which was part of Tonbridge town on the eastern side of the High Street, between the Lower Bridge and Brook Street Lane)
Ref:  HO.107/1615 - page 32
I also came across another JOY family where the father was also born at Brenchley so didn't know if they were too do with your family tree so have included them as well.
Henry Joy   Head   M   31  ?ra??er           K.Brenchley
Mary Joy     Wife    M   31  ?ra??er Wife   K.Wrotham
Henry         Son     U     4   Scholar           K.Tonbridge
Benjamin Thorne   Lodger   U   23   Coachman   K.Tonbridge
Mary Steel   Serv.   U   10   House Servant   K.Tonbridge
All living at 55 High Street, Booking Office.  (This would have been over the road from William and his family)
Ref: HO.107/1615 - page 15
Hope this gives you the information you was seeking.
Regards
Lindy Lou