Douglas,looked for a birth for Thomas and found none.I only found a Robert in co Tyrone in 1821 but believe he went to New York.As for Margaret Meagher,the surname is so numerous you would need more identifying info to locate her birth.I found 2 arrival records which may be of use.
Mr and wife Spiller arrival port:Hobart arrival date:25 August 1833 departed from:Liverpool on 7 May 1833 ship:Cabotia
William Spiller and son arrival port:Hobart arrival date:6 January 1843 departed from:South Australia on 24 December 1842 ship:Emma
Also found this marriage; Robert Lent married Margaret Spiller 20 July 1848 in Hobart maybe she is related? Hope something is useful,Kim