I have in my family tree two Seymor familes that may have had Devon conections though the census records say they were born in Beaufort, Essex. England.
William Henry Seymour born abt 1821 died abt 1855
he married Elzabeth Harris b 1821, Devonport, d. abt 1855
He was a tailor and lived in St Pancras, London
John Wiloughby Seymour was his brother, born abt 1821
he married Elizabeth Alden Hewins and they lived in Boston, Massachsetts. I think he was an artist as was Elizabeth's father Amasa Hewins.
Their children were born in the 1846 to 1853 range.
The family legend says they were related to the line that became the Dukes of Somerset in the 1920's but I haven't traced it back before those brothers.