I understand your frustration. Last year, a collection agency working for a company I do not owe money to (having paid off the loan 7 years ago) contacted my ex-husband of 14 years at his home I never shared with him in a different city and county and phone number than where we lived when we were married. All this because at the time I took out the loan, he was listed as my next of kin (still my spouse at that time). He didn't give them any information. I had also remarried several years ago and lived in another state! This collection agency had my address and correct name as well.
Collection agencies will harass anyone they think is connected to you in any way, especially if they are not making headway with you. It's all about intimidation. Your brother can send them a certified letter telling them they do not have permission to contact him again. You can also send them a certified letter telling them they cannot talk to you or anyone else, connected to you or not. Under Title VIII they must comply, but anything not communicated by certified letter will be ignored if at all possible.
What is the pain about this is how they get the information in the first place. Among other services, Intellus.com gives tons of information, a bit of it for free, much more if you pay a fee. They can track a person by aliases, possible past addresses, possible phone numbers, possible employers, possible criminal records, possible relatives, etc. Note I said "Possible." This is because services like Intellus do not guarantee the correctness of the information theysupply (even for a fee) and the fine print suggests you verify the information. But an amazing amount of "possible" information is out there. Under my husband's name, possible relatives included his mother, deceased father, sister, brother-in-law, brother, sister-in-law, nephews, underage nieces, and his ex-wife. My name showed not only my ex-husband as a possible relative, but also HIS new wife. It's nuts.