Hi Malea,
That 1884 will you looked at was for Margaret COWLE / FARGHER the widow of John RADCLIFFE 1785-1859 of Belfast, Andreas.
John Radcliffe, widower, m. Margaret Faragher, widow of Maughold, in 1833. (Margaret was the widow of Thomas Faragher, and daughter of John Cowle of Bride, according to Constance Radcliffe.)
One of their children was Margaret RADCLIFFE bapt.15 Nov.1834 Andreas, who married 1 Jan.1859 William KNEEN Lezayre [KNEAN on IGI]. The "new" IOM Parish Registers search on familysearch gives his father as Daniel Kneen and hers as John Radcliffe.
Margaret Radcliffe's 1884 will has "with pledges William Garret of Cronk e Mona and William Kneen of Seabridge House in the parish of Lezayre". (This address coincides with his 1881 census entry address on Familysearch, of "Lea Bridge Cottage" Lezayre, where he is with wife Margaret aged 46.)
Her will mentions both her daughter Margaret Kneen, and her granddaughter Margaret Kneen. I can't see any children recorded for her daughter Margaret and husband William Kneen, but as John Radcliffe had nine children by his two marriages she could have been a child (perhaps illegitimate) of any of their daughters. She may also have had children with her first husband who could be worth following up, as they would also have Margaret Radcliffe as their grandmother. Censuses are probably the best source.
Sue