E-mail via PM. In the meantime, Robert Kerr and the "new" family did emigrate. In 1871, Robert and Margaret, and children Janet, Robert, Joseph, 3, and James, 1 month, are living in Caledonia, Haldimand, Ontario. In 1881, there's another child, Margaret, 3, as well as the others. Janet married Henry Falkal in 1881. She died Detroit, Wayne Co., MI, in 1932, a widow. Robert (Jr.), married Isabella Lyons in 1884. After she died in 1897, he married Rachel Denny. Robert (Jr.) died in 1935 and is buried with his two wives in Woodstock Presbyterian Cemetery, Woodstock, Oxford, Ontario. I see Robert Jr. after the 1881 censuses, but not his parents. And nothing's jumping out for Joseph, James and Margaret. Nothing more is turning up for them online there in Woodstock. There is a private online tree at Ancestry with these families. I've e-mailed the owner. No evidence so far that Thomas and Mary rejoined their father in Canada.