Thank you all so much.
You have found two marriages which seem relevant to my Kennedy family.

They must be father and son marriages.
Watson Kennedy and Isabella have a son Watson Kennedy, Aged 6, living at 13 Old Glenarm Road, Larne, Co. Antrim in the 1901 census provided to me by another very helpful Rootschatter.
I wonder what became of the son Watson and his wife Jane. My grandparents Hessie Kennedy and Charles Taylor were married at St. Anne's, Belfast so I think the young Watson must have been my grandmother's brother.
I have just looked through my notes and found a record I downloaded ages ago. It is a death record for Watson Kennedy - date of death - 1/12/1961. He was 68, married, a labourer, living at 5 Matlock Street. He is buried in Glenalina Cemetery and the grave owner is down as JEAN KENNEDY. I had no idea who Jean Kennedy was but with you finding a marriage for a Watson Kennedy to a Jean Greer this grave may be that of my grandmother Hessie's brother.
The trouble with family researching, it goes on and on with lots of surprises. Thanks
Maeabbie
Thanks also for giving me Watson Kennedy senior's father's name of William.