I've just stumbled across this after googling Smart and Campbell.
I am descended from the Smart family and my Grandmother was a Campbell Sloan. Her mother, a Campbell Smart, was born and lived on Tidenham Chase at Firgrove.
The Campbell connection is to do with Jamaica (Archibald was a governer I think) and we had a portrait of one of the young Smarts being rescued from an alligator in Kingston.
My father thought the Campbells and Smarts were probably friends, but in the past I have stumbled across a link from an old newspaper reproting on the young Smarts and their Uncle Campbell in Jamaica. I have letters from Francis Smart to his wife in Powder House Farm, Tutshill, near Chepstow and one of my great, great uncles (I think a William Smart) lived at Oak Cliff in Woodcroft before moving to Bristol or Bath as an old man in the late 1800s or early 1900s. He was remembered by an old lady who lived near Tidenham when I was a little girl in the 1960s, being driven down the road in his horse and carriage. She was a little girl at that time and he, an elderly man.
I lived in Tidenham as a child and, in my teems, rang the bells at Tidenham Church, one of which was given to the church by a Smart who was church warden - probably in the 1800s. There is also a gravestone in the belfry with other Smarts on it (more of the family) but difficult to see now because of countless bellringers standing on it.
Tidenham Church has grave stones in the boundary wall for several Smarts from the 1600s. One was Mary Tudor Smart and others had the usual Smart names - John, William, Elizabeth, Mary. My Grandmother was Elizabeth Mary Campbell Sloan, Her mother was Eliza Mary Campbell Gee (nee Smart).
I don't know of any Watkins's in the family, but have a friend who is a Watkins and we were at school together.
I don't know if you're still looking for link to the Watkins family, but let me know and I can try to find out more from my friend.