When your brother is initially hired he has a short time period during which he can sign up his parents/spouse/dependents and friend(s) to his flight priveleges. After that short time period elapses (don't know how long it is, maybe a month), he can ONLY make changes once per year, normally at the very beginning of the year. He can't make changes throughout the year, but only during that annual enrolement/update period. He will get an email from the pass travel department letting him know the steps (it's basically a web-form that's filled out on the company intranet under the passtravel section of the site).