Hi Colin,
I did find the christening for Margaret Shimmin daughter of John Shimmin & Ann Gell 4 Sep 1808, entry 30 of page 57 on the IGI film 0106738
I also was viewing the 1861 Douglas Census
Class RG9; Piece 4417; Folio 8, Page 10 - GSU 850886
Address 15 Cjt Nelson St.
Ann Eastman Head - age 61 (1800) Grocer & Provisions dealer
Margaret Cubbon - sister - age 59 (1802) Patrick, Farm Laborers Wife
William Shimmin - brother- age 52 (1809) Patrick Slater & Plasterer
Margaret Quayle - niece- age 22 (1839) Dressmaker
This seems to tie together with the 1841 cenus which I posted previously - am wondering if the Margaret Cubbon above was married previously to Philip Quayle and this is her daughter Margaret listed below - if Margaret is the daughter of John Shimmin & Ann Gell, then the father of John Shimmin is Thomas & ? see 1841 census previously.
Tim