Trying to sue in Denver for boiler issues

[Kyle L.]

My brother is dealing with someone trying to sue them for problems with the house that happened 11 months after they sold it. I just wanted to see if anyone else has ever dealt with something like this. Here is that back sorry. Home in Littleton Colorado was sold in July 2016. Before the home was sold the new owners had it inspected and they wanted the boiler services and cleaned. So my brother had it cleaned and the purchaser signed off on it. In May 2017 the boiler had a backdraft and the carbon monoxide detector when off in the utility room when off so they evacuated the home and called the fire department. The family ( mother/father in there mid 30's and 3 year old son) said they felt fine and no one vomited so they didn't go to the ER. Then 10-15 days later the mother and father went in and started seeking medical treatment for carbon monoxide poisoning. There was never anything mentioned about there kid. But now they are trying to sue my brother for $44k for damages and pain/suffering. My brother lived there for 6 years and never had a problem and it obviously worked fine for this new family all winter and now this happens. Any thoughts, ideas? They are also trying to sue my brothers realtor and their realtor.