Legal Question in Family Law in South Carolina

Probably not.

Except when you're representing yourself, practicing law without a license is illegal. In S.C., unauthorized practice of law is actually a felony, with a penalty of up to five years in prison and/or five a thousand dollar fine, and the law specifically prohibits the representation of another even if you have permission from a court. And, while it's unclear from the question whether this person is seeking payment, whether or not this person is paid for his or her services is irrelevant for purposes of the prohibition on practicing without a license.

I would want to know more about the specifics of exactly who this person is and what services they are offering, but it sounds like you may be dealing with someone who is potentially breaking the law.

Furthermore, this "legal negotiator" may or may not have the knowledge necessary to effectively represent you, and could end up doing more harm than good. I would strongly encourage both parties to seek the advice of an attorney before moving forward with this arrangement.