Trustees can either be natural persons or a body corporate (ie a company).
If the original Trust Deed prescribes the number of Trustees then it would be a Breach of Trust to administer the fund with a different number of trustees.
The Trust Deed should also prescribe who has the power to appoint and remove the trustees from office, as well as who has the power to vary the number of trustees.
The question of replacing three natural person trustees with a sole corporate trustee was considered by the Supreme Court of New South Wales in Re J.T.C. Mayne (Dec) (1928) 28 SR 157, pursuant a summons for advice under Section 63 of the Trustee Act 1925 (NSW).
The Court held that under the terms of the trust a corporate trustee could be appointed as a trustee, however another two persons would still need to be appointed as trustees to comply with the terms of the trust. The Court held that the appointment of only one trustee would amount to a Breach of Trust
The Court then stated that an application could be made under Section 81 of the Trustee Act 1925 (NSW) to have the terms of the trust amended to allow for a sole corporate Trustee.