My daughter is in a custody battle right now and we have a GAL, he is an attorney, for her two children that is so biased he is unprofessional. He never researched or documented my daughters family only taking into account what her ex husband and wife story which is fabricated or blown out of proportion. I can't go into details, but if he keeps on abusing his power with the judge I will have to sue him for harassment and unprofessional conduct.
I hate to tell you that you can not sue him. He is protected. However you can file a complaint against him with the G.A.L. office. It will not guarantee that anything will be done but, this is your only course of action you can take against him.