Haven't received as yet, but I believe the clue is in the 1881 census where an Eliza Roberts aged 15 is shown as niece, I think she is the daughter of Samuel (Thomas's brother) and Esther,
and then Samuel and Thomas are the sons of Samuel (who was also a boatman) and Ann Roberts and because of occupation they travelled extensively, looks like Thomas was born in Nottingham and not Coventry. Hopefully the marriage certificate will show the father as Samuel Roberts a Boatman.
Thanks for your help