Wendy,
You might find William's baptism in the relevant church records, assuming you know his precise denomination. RC records are mostly on-line on the nli site:
https://www.nli.ie/en/family-history-introduction.aspx
For other denominations, the churches usually hold the originals but there are also copies in PRONI, the public record office, in Belfast. A personal visit is required to access them. Access to the records there is free. This link explains what records exist, parish by parish:
https://www.nidirect.gov.uk/publications/proni-guide-church-records
If you are unable to go yourself, you could employ a researcher. Researchers in the PRONI area: http://sgni.net
George Sloane’s death in 1871:
https://civilrecords.irishgenealogy.ie/churchrecords/images/deaths_retu…