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At this point there is little he can do since there is already a warrant. He will need to turn himself in at the hearing and explain the situation. Keep in mind since he is currently paying support the judge is going to want to see this continue....if he goes to jail he loses his job and thus support will stop. Make sure you mention this to the judge at the hearing.
Often if you can offer up a lump sum even if it is small the judge will allow him to be released from jail. As for mom she can request that the charges be dropped but that doesn't look like it will happen so at this point he will have to go to jail. If the judge wants to he can let him out the same day since he is currently paying support.