You said: From the few pages I looked at I couldn't see what Estate they were on. You can try www.landedestates.ie
and see if any ring a bell
It looks like the tithe book entries correspond to the Willsbrook House near Castlereagh, in the general area of Cloondacarra.
At least I have an interesting location, but no way to prove whether these particular Thomas and Patrick Shannon are the right people. I will have to look at other circumstantial evidence, like wives' names.