While one can change the paperwork in the Trust Indenture to require only one trustee, the paperwork is designed to have three trustees for the following reasons:
1) If multiple trusts get called into court, due to their normal interactions in business and trade, it is best to have unique representatives for each trust. A trust that transfers assets to another trust, should have two unique trustees signing the paperwork - otherwise a single person/signature for BOTH TRUSTS could cause the court to see each trust as being "one trust" OR it could fall under a "conflict of interest" issue in the eyes of the court;
2) If there is a violation by a trustee, there is still two remaining trustees in control, which the judge/jury look upon with clemency (mercy) when judging a trust (so it is not in-persona conjucta);
3) If a single trustee is legally removed by a court action, the remaining trustees take over without the court being required to obtain a new trustee (per their judgement), thus avoiding the dissolution of it and still keeping it in one's control.
NOTE: Even if one is removed from the trust. As long as there is one other trustee that can be trusted, the trustee can take action to vest (trust assets are distributed) and a new trust can be started with all three original trustees.