Here's a possible obituary for Joseph and Sarah's son George Crossett, it's in the Mid-Ulster Mail of 16 December 1950, it indicates that a substantial chunk of this branch of the family headed out to Canada, I've omitted the names of the younger family members mentioned in the obituary in case there is any possibility that they are still alive, I can pm you that fuller information if you require.
MR. GEORGE CROSSETT.
The death took place on 10th November, of Mr. George Crossett of 312 McMaster's Avenue, Turtle Creek, Canada, after a long illness. Mr Crossett was a native of Cookstown, but emigrated to Canada many years ago ... ... Surviving are his widow, Maggie Davidson Crossett ... three daughters ... three sons ... two grandchildren ... four sisters - Miss Sarah Crossett of Church Street, Cookstown, Mrs. Lizzie Currie, of New Jersey, and Mrs. Mary Hewitt and Miss Helen Crossett, both of Toronto, Canada ; and a brother Joseph Crossett, also of Toronto. The burial was in William Penn Cemetery, Turtle Creek.
So it's starting to look like Sarah was the last child of Joseph Crossett and Sarah Sloan to remain in Cookstown - at least until 1950 - and it looks like she didn't marry.