if they arrived in England during the Famines of the 1840s and 1850s then you should look at their entries on the English Census returns right up until 1911 to see if any of them had their actual birth village/town recorded on their entrym this is the usual best starting point with Irish genealogy. Once you haqve identified a location, I could be more specific on whether you will be able to use original sources or would have to use the substitute sources, as many records were destroyed for Irish families.
Start by using this site:
familysearch.org
for them and see what you discover.