Yes, one can use the same trustees for all trusts created. The legal reasoning behind having (3) trustees, is due to the fact that having 50% control or more of a trust as trustee can lead to undesirable results when defending a trust in court. Further, if 2 trusts are called into court due to interacting with each other, a judge will want to see 2 unique individuals standing there in court to represent each trust. If there is only one trustee, representing both trusts - it would not pass "The Smell Test" and be deemed potentially fraudulent by the judge (even when it is not).
NOTE: Due to the privacy agreement within the Trust Indenture (a private contract), no trustee can be forced by law (per U.S. Constitution Art. I Sec. X Clause I) to reveal any other trustees which sit on the Board of Trustees. Only one trustee need be in court to defend the trust.