I hadn't read your byline, but it now seems certain that the May V Seaborne who married Thomas Watkins in 1930 was the May Victoria Seaborn who was born in Jan-Mar 1930. She was born in Penrhos to (Ernest) James and Mary Ann Seaborn (nee Tedstone), and she had nine siblings. They are Ernest James, George Henry, Thomas J (1913), Frederick W S (1915) and five others born in Abergavenny. They may still be alive, so I can't name them but, if you search on the freebmd.org.uk site for children called Seaborn with the mother's maiden name as Tedstone, they will come up. Ernest James Seaborn and Mary Tedstone married in 1907 (although there is a transcription error on the freebmd site so I don't think the marriage will show).
(Ernest) James Seaborn (called Jim in 1901) and earlier generations can be traced on the censuses if you want that information. Their names switches between Seaborn/Seaborne/Seabourne.
Tracing James Norgrove will be much harder. One candidate may be the Henry James Norgrove who was born in Mardy, Glamorgan in 1905 and died in Swindon in 1967 (having married there in 1942). His wife didn't die until 1998, but her name isn't on his memorial stone (which doesn't give any more information). They had several children. That said, he's probably not the right person anyway.
Richard