How on Earth, 5+ years after the devastating collapse of collateralized mortgages, would any plan fiduciary permit their plan to hold so much money in mortgages?
Your item #4 sounds like a breach of fiduciary prudence to me.
If they're going to talk to a lawyer as indicated in item #1, you should advise they be sure it's a firm w/ someone well versed in ERISA because I suspect they'll be filing something w/ the IRS or DOL by the time this is done.