A lot of emigrants went to Canada as it was cheaper passage than to USA. You can find information on line about Canada.
Use a resource website such as: www.cyndislist.com
You might find information about Nova Scotia onwww.theshipslist.com
Is Sligo where they are from or just posting for Ireland?
There are few resources prior to 1859, even church parish records would be sparse.www.rootsireland.ie
PAY website - not for Profit Foundationwww.genealogy.nationalarchives.ie
1846-1864 depending on County
1858 for Sligo