In some states, the court can designate an educational surrogate parent, or something similar, who is kind of like a GAL specifically for educational decisions. I don't know how it works exactly in divorce/separation cases, but in many state custody situations, there is both an ed surrogate parent and an ed advocate appointed by the courts. So one for decision-making, and one for advising. The ed advocate is usually someone with expertise in special education (special needs teacher, psychologist, speech therapist, etc.). You might investigate whether there is an existing system of this kind in your state.
As to some other kind of professional, I would agree that having 2e skills is critical. I would lean toward some kind of professional psychologist (neuro or school would be my personal bias).
