Griffiths Valuation for 1860 lists just 1 William Nelson in Kilskeery parish. He was a farmer who lived in Derrymacanna townland. He had plot 3 which was a 40 acre farm. That farm today is on the modern Stralongford Rd which is a few miles east of Irvinestown towards Trillick. Looking at the property on Google Earth it still appears to be a farm today.
http://www.askaboutireland.ie/griffith-valuation/index.xml?action=nameSearch
I found a death for this William in 1875, aged 73:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1875/020614/7232587.pdf
The informant was Jane Nelson which fits with the information you have provided. Jane died in 1888. The informant was her son Richard:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_returns/deaths_1888/06187/4769020.pdf
Family here in 1901 census. Likely brothers for your Joseph William Nelson:
http://www.census.nationalarchives.ie/pages/1901/Tyrone/Moorefield/Derrymacanna/1740926/
Same property in 1911:
http://www.census.nationalarchives.ie/pages/1911/Tyrone/Moorfield/Derrymacanna/869678/
John James Nelson’s marriage in 1902:
https://civilrecords.irishgenealogy.ie/churchrecords/images/marriage_returns/marriages_1902/10261/5734673.pdf
Probate of the Will of Richard Nelson late of Derrymacanna Trillick County Tyrone Farmer who died 4 December 1915 granted at Londonderry to John James Nelson Farmer.
Eliza Nelson died 1884 aged 24, sister to Richard. Derry Journal of 15.2.1884 reports her death and says her father was William Nelson and that she was his youngest daughter, so there is clearly at least 1 more:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retu…
Family appear to have been Church of Ireland. Kilskeery COI records start in 1767. There’s a copy in PRONI (the public record office) in Belfast. The records have been indexed there.
