Carter Higgins Sweet

I am still no nearer to any further information on my G G.Grandies. William was B 1854 to George + Elizabeth Sweet. William. M. Margaret Higgins in Australia 1879.IT is the Parent's of these two that I have trouble with.
Williams parents as above. Margarets as follows. John Higgins + Johanna Carroll. Carters from LEISTER. HIGGINS from TIPPERARY IRE.