Hi Nicky,
I don't think they were brothers. But I do think it very likely they were cousins. So far I only have one sibling for my Robert, named William. I do know that Robert had 2 nephews come to Canada, so I do know he had at least one sibling. And one of those nephews, James, named his daughter Agnes King Matthews, presumably after her grandmother. So I am fairly confident that Agnes King was the mother of my Robert. Now to piece together the rest of the family!