I have a feeling that the Sarah Belvin in the 1881 census with the Kellys is the same Sarah Bevlin in the 1871 East Hastings census and the same Sarah Bevline in the 1861 East Hasting census with her husband John. The ages match up.
There is a John Devlin in the 1851, 1861 and 1871 Otonabee, Peterborough censuses, who was born c1807 in Ireland. It appears he was married to Ann Fahey(?), who was born c1822 in Ireland. She was deceased prior to the 1861 census. Children mentioned in the censuses are Mary c1841, James c1843, Roger c1846, Patrick c1848 and William John c1852. William John also appears, for a second time, with his grandparents Roger and Ellen Fahy in the 1861 Peterborough census.