This depends on the individual bank one is opening an account with. For example Chase requires a Successor Trustee, but TD Ameritrade requires a Co-Trustee, and other banks only require one Trustee to sign. Call the bank before the appointment to verify what they require for trustee organization! A Successor Trustee being the person who takes over when a Trustee is incapacitated, a Co-Trustee being a person who makes mutual decisions regarding the trust.