If your brother didn't register his name as a domain, then that is his problem. This happens all the time. The guy owns the domain. If your brother wants it, he can buy from him.
As for saying your brother is involved, that is wrong.
ETA: IIRC this happened to American Idol. They didn't register the domains of contestant names and then normal everyday people did. They had to pay big bucks to the people who purchased the domains. Now, they register the domains when they know the contestants.
Not to get into legalities, but this isn't strictly true. Cyber squatters bank on getting big bucks for domain names rich companies miss, of course, but I can't just jump on Disney.com (assuming they were stupid enough to let the domain expire) and then hold it for ransom - a judge would say that Disney had more right to the name than I did and force me to hand it over. Look up the saga of Mike Rowe Soft, who registered a domain in his own name and lost it
His name was Mike Rowe, not Mike Rowe Soft....
True - but looking up Mike Rowe just gets you the Dirty Jobs guy