Claiming Children on Taxes

A mother and biological father share custody of a 13 year old. The step dad (no longer married to the mother) has been awarded rights as a psychological parent . The step dad and mother each pay for all of the child’s activities and medical bills. However, the step dad does NOT pay child support. The biological father pays child support but not on a regular basis and is always in arrears. In accordance with the court order, the step dad has equal parental rights as the mother and biological father, but because he isn’t ordered to pay child support, he cannot claim the child as a dependent, medical bills or any activities on his taxes. Can the step dad have the order modified to show that he is obligated to pay child support (and actually pays it) in order to claim the child on taxes?