Resignation of a trustee (co-trustee in this case) can be accomplished in various ways and only one of the following procedures needs to be selected.1) Resignation according to the applicable provision in the trust.2) In the case of a revocable trust, with the consent of the person holding the power to revoke the trust. (Since this is a family trust, the trust provisions may authorize the creator of the trust also called the settlor to have the power to revoke the trust).3) If the trust is not revocable, with the consent of all adult beneficiaries  who are receiving or are entitled to receive income under the trust or to receive a distribution of principal if the trust were terminated at the time consent is sought.  If a beneficiary has a conservator or attorney-in-fact, consent to the trustee's resignation should be obtained from them instead of the beneficiary.4) Pursuant to a court order.If you select 1 or 2 or 3 above, there should not be any cost.  If you select 4, there will be court filing fees and other court costs.  It would be advisable to select 1 or 2 or 3.  You can do this yourselves.  Have the resignation and acceptance of the resignation in writing.  A trust only needs one trustee.