From what little I understand, the godparents are supposed to help raise the child/children in the faith. If you find out later on that they are not Catholic, I cannot see how this would not be a problem. If you know beforehand that they are not Catholic, I would think it be upon you to find godparents who in fact are Catholic.
This seems to be a question to bring to your Father (priest, just in case I’m using Father wrongly).