Hi, Christine. William and Brian don't have profiles at Wikitree, so it's difficult to know what sources you've already used or to suggest others which might be helpful.
Ancestry has a marriage record for William Kenny (pointsman, age 24, son of Brian Kenny, agent) to Rosina Osborn in Tower Hamlets in 1868. Would these be yours? Do you know if Brian had other children, where they were born, whether he was married in England or Ireland? Collecting more information about others in the family might help to piece together Brian's background and point you to his family in Ireland.
EDIT : I've added a profile for William at Kenny-3036