Sorry, the facts aren't entirely clear. I gather from what you have stated that you have a letter from your lawyer? That states that you and grandparents have certain rights in relation to the child? Is the letter confirming an agreement between the parties regarding your rights? Who is the letter addressed to? And who does the lawyer act for?
If the letter doesn't reflect an agreement between the parties then it cannot be registered with the court. In order something to be enforceable by the court - the court needs to have made the orders themselves (i.e. on application by you for orders) or else the orders must have been made by the consent of the parties.