Generally speaking grandparents do not have visitation rights. If they want to have visitation with the grandchildren then they need to seek to be joined to the family law cause of action and then file a request for order regarding visitation.
Even if the grandparents meet the criteria to be joined, the court has discretion to grant or deny the motion to be joined as a party. One significant thing they look for is whether or not the grandparent is bonded with the grandchildren. One test to determine the amount of bonding is the amount of contact they have with the grandchildren.