Split interest trusts (lifetime income beneficiary, future remainder beneficiaries) have a built-in conflict of interest (income beneficiaries prefer income and remainder beneficiaries prefer growth). However, when you add a blended family to the mix, the conflicts become more apparent. Further, the discretion trustees are frequently granted to make discretionary distributions of principal may exacerbate this conflict.
These situations would frequently call for a disinterested 3rd party trustee that has duties to be fair and impartial to both current and future beneficiaries. Having you and the step-mother serve as co-trustees was probably an attempt to mitigatae this conflict by having both current and future beneficiaries represented in the decision process.
Consult with the attorney that represented your father (or seek independent representation of the attorney also represents your step-mother) and get direction on the specific duties of the trustee (the discretionary authorities, the reporting responsibilities, etc) and make a decision based on facts and your father's intent. An alternative may be to have both you and your step-mother resign in favor of an impartial 3rd party trustee.
If you have accepted your role as Co-Trustee then you have a duty to be smart about managing other people's money.
Before you make any decisions you should consult with an attorney without your step mother present to give you candid advice as to your options.
You can look to this website or to naela.org for attorneys who practice trust and estate law and who have an office near you. Good Luck!
Legal Disclaimer: Paul A. Smolinski is licensed to practice law in the State of Illinois only, and as such, his answers to AVVO inquiries are based on his understanding of Illinois law only. His answers are for general information about perceived legal issues within this question only and no response to any posted inquiry should be deemed to extend any right of confidentiality between you and Mr. Smolinski, to constitute legal advice, or create an attorney/client or other contractual relationship. An attorney/client relationship is formed only by specific agreement including an evaluation of the specific legal problem and review of all the facts and documents at issue. We try to insure the accuracy of this information, but we cannot guarantee its accuracy. The reader should never assume that this information applies to his or her specific situation or constitutes legal advice. Therefore, please consult competent counsel that practices in the subject area in your jurisdiction and who is familiar with your specific facts and all of the circumstances.