Did your friend try contacting the airline directly to see if they could issue a gate pass or someway of meeting the brother in-transit? Maybe stress it is to the help the brother get to the next gate, get him some food, etc. etc.?
I know I can use the local airport's currency exchange if I'm not flying by getting an airport 'ambassador' to escort me to the office (and a checkin at the Operations Office). And even
LAX's website suggests that might be an option:
Can I wait at the gate for passengers? If not, where can I wait?
No. Federal regulations now prohibit non-ticketed persons beyond passenger security screening at all U.S. airports. Please meet your arriving party in the terminal baggage claim area or terminal curbside. Announcements are made to arriving passengers that they can meet their welcoming parties in these two areas. Airlines will accommodate requests by individuals meeting passengers with special needs, elderly, and unaccompanied minors. Please check with the airlines directly.