Your brother is the "Substitute Trustee" and is required to provide a complete accounting of your father's estate at least once a year. You are entitled to a copy of the trust agreement, and all relevant information including: 1. Trust assets. 2. Trust Expenses and 3. Trust Income. He should have also filed a final income tax return for your father and ongoing income tax returns for the trust.
If your brother fails to cooperate the you and your other brothers can file a petition for accounting and get a court order requiring production of the accounting, and possibly also petition to have the younger brother removed.