Sorry, I can't really help..........
The period you are talking about is the time of the Famine 1846-1851.
I have 3 FEE brothers born in Fermanagh between 1790-1799 that could have had a brother named Thomas.
The earliest FEE emigration I have to Scotland is around 1900 to Glasgow.
There are lots of McTiernans in Ireland in the 1901 Census, but none in Fermanagh.