Best advice would be for your brother to hire an attorney familiar with these issues. Sounds like a bit of a frivolous lawsuit but best to protect yourself through the correct legal entities.
2nd best advice: Delete this thread. You'd be suprised the lengths people go to when suing, etc. Lawyer up and zip it.
@Kyle L. I've had CO poisoning and it does not last 10 days unless you are re-exposed to CO. In reality, they are probably trying to get the cost of the attorney and a new boiler. I can tell you this, it won't take long to eat up $44k in attorney fees. Not sure how to advise you but if it goes to court I don't see anyone but the attorney's winning.