Family Search pilot:
Marriage 1870- Ballinrobe Frances Tantrim and Stewart Hewitt
baptism- Cappaduff 1871 Louisa Mary Hewitt- mother Frances Eveline Tantrum -father Stewart Hewitt
These are the only Tantrums in Mayo

I think Fanny is in earlier censuses in England and in 1901, Stewart Hewitt (born Westmeath) is in Aston (coincidence) with daughter Louisa Bills, 2 other Hewitts born Belfast and Prt Stewart, Ireland and Stewart is a Missionary of S R S of Ireland

I know this has nothing to do with your James and Edward but it does add a bit to them! (juts don't ask me what

)
The site also has a marriage:
1859 Crossboyne Mayo- Ann Mernagh (father Edward) and Robert Parham.
IGI has several children to this couple -each one a different surname for Ann (variations)