I have changed the classification of your question to help you get better answers. This is not an estate planning issue. And I don't believe it is a guardianship issue. I believe you are stating that you and your husband are the managing conservators for your grandchildren but that he is not their grandfather. I would have thought that one or both of the actual parents had been ordered to pay child support. A divorce between you and your husband would not result in an order to pay child support by one of you to the other.
DISCLAIMER: This is not specific legal advice and does not establish an attorney/client relationship.