Hi Rosie,
Looks like you're missing some information here. You haven't mentioned the departure airport. The departure airport plays an important role in claiming compensation from American Airline. If your brother would have departed from an EU airport then the following rules apply:
According to the EC Regulation 261/2004, "you can claim compensation if your flight was cancelled without notice or with a very short notice. Also, in the event of a cancellation, the airline is responsible for providing passengers with the following:
- A minimum of 2 telephone calls, fax, emails or messages
- If you are provided with an alternative flight whereby the time of departure is delayed by a day or so, the airline should provide you with hotel accommodation and transport between the airport and place of accommodation."
Contact American Airlines customer support or visit their website (https://www.aa.com/i18n/customer-service/support/customer-service-plan.jsp) for more information on assistance on flight delay compensation.