Don't complain at this point. If they think there is a possibility of a reasonable resolution, that is preferable to risking a jury verdict. You do not have to settle but doesn't hurt to try again.
Your brother needs to ask his lawyer this question. No one here can second-guess his lawyer.
Attorney Inga Stevens is licensed in Maine. She provides general information on Avvo.com. No attorney-client relationship arises out of the information given here.
All mediators are different and handle things a little differently. I have had mediators call me up and still work toward getting the case resolved even after a formal mediation. Meeting with parties separately is necessary. Many times the mediator has to "hammer" on one party or another, and does it in private. It sounds like your mediator is doing what he can to try to bring the case to a successful conclusion. Let him do his job.