Property mediation

Let me give you all the info…and then hopefully you can help answer my question.

Wife is wanting two houses out of divorce when they (both) legally put houses in son’s name 2 yrs ago
Son got “named” on the divorce lawsuit (as well as the husband) since his name is on the houses in which the wife (his mom) wants

Husband and wife got served mediation papers stating the date and time
They went to mediation for 3 hrs and the cost was $600

Mediator told husband that he had good news. He said he could defray the cost of mediation cause he was going to bill the son (who wasn’t at mediation nor was he served) for 1/3 of the cost ($200).

Is this legal?? Can the son be charged for mediation when he wasn’t even there nor knew nothing about it??? Mediator said he was a “third” party on the divorce case…and that was his logic.

Nothing was even discussed in mediation about the 2 houses because she KNOWS she doesn’t have a chance to get them. Yet the son is going to get billed for part of their mediation just because his name is on the divorce case??

Husband is ready to report mediator to the state bar.

There is no such thing as being served with mediation papers, and the son cannot be billed.