I have some information about a William Kelly who married a Ruth Scott (my mother was a Scott). They had 4 children - Bob and Maggie (twins), Eliza, and Jack. William died in 1892.
The Scott family was also from Tyrone Co.
William Scott, Ruth's older brother, married Margaret Bell. Witnesses were William and MaryJane Bell. William and Margaret were were my g. grandparents.
Ruth's younger brother married a Sarah Bell in 1880. Witnesses were Almon Monteith and Annie Bell.
I'm not sure how this fits into your research, but with all these similar names from Middlesev County, there must be a connection somewhere. Let me know if I can be of any further help.