Thanks for your message on the Sligo message board? Do you have any more information about your ancestors, such as if they were had kids, where the kids were based, what they worked at?
Did they ever return to Ireland?
There are a number of records in the 1911 Census for "Henry Brett". Perhaps that person is related to your Henry Brett? If so, you probably still have many relations in Sligo.
My guess is that others will sign on soon and flesh this out more for you.