I have 2 Godmothers and 1 Godfather. 1 Godmother is a cousin who I see like once a year and don't maintain contact with, despite living in the same village! My other Godmother was a friend of my mother, I grew up with her daughter and we were close but I haven't seen or spoken to her for about...5/6 years. My Godfather is my uncle (my mums brother) and he is the one I see most.
You get them when you are Christened...so were Michael's children Christened and are christian or more specifically catholic?
They are present at the Christening or Baptism of a baby and promise to help raise the child in a Christian manner. They also are called to be present at Confirmation.
I think they were supposed to care for you if your parents die - but it never happens now.
Their role is simply to be there for the children really.
But as Elusive says, nowadays its just a title parents give to one of their friends, and other than being a witness for the christening or baptism.. and possibly confirmation they do basically nothing else.