Seems to me its a good possibility that Thomas and Samuel could be brothers. Thomas has a "fluid" birthday, different on census and headstone, but that John Splane in Beckwith sounds interesting.
Did he stay in Beckwith long or move on?
The dates I have are John Splan (1802 - 1886) married 1845 to Mary Webb (1826 - 1903). Her (presumed) brother John Webb (1799 - 1884) married 1834 Elizabeth Splan (1803 - 1890). They are buried in adjoining plots at St. John's, Castlemore.
Now I wonder if our John (born 1802) could have patented land in Beckwith in the early 1820s? I'll try and check the Patents, etc. at the Provincial Archives for clues.
I'm sure there is a connection just because of the rarity of Splan / Splaine as a name, even in Ireland.
I guess if we could find some of the appropriate registers in Cork, we find a connection.
As they say, "more research required" but there are certainly a lot coincidences that keep it intriguing.
I'll keep you posted