As far as I know, the only role of Godparents after the christening (this is what they agree to at the christening) is that anything happens to you and your partner, they will make sure that your child is brought up according to your religious beliefs.

I don't think they are the legal next-in-line gaurdians, unless you specify that in your will. My godmother was my brother-in-law's mother, but my legal gaurdian was my sister, so I think that is up to you. I don't think naming someone as godparents qualifies as legal anything, because a child isn't required to have godparents unless you are religious.

My brother was my godfather, and he and my godmother never really did anything, except my godmother gave me a present on my first communion. (My brother would have anyway.) Other than that, they had no real impact on my life. (Except my brother, doing brother things)