We need more information to be able to completely answer your question. First, is your mother living? Your mother has a minimum right of inheritance based on the estate planning documents (the trust for example) or what is called the elective share, unless she waived her rights in a marital agreement. If your mother is not living, then you may be able to inherit based on your status as her daughter - it depends on how the estate plan was drawn up.
As it concerns your rights as a beneficiary under an insurance contract, the insurance carrier will only make the payment to you. If the personal representative (not the trustee) of your step-father's estate is in possession of the insurance contract you can demand that they provide those documents to you if you have a legal interest (you are a beneficiary) under the policy.
Your stepbrother cannot change the policy, unless it was your father's desire to do so before he died, and your brother had the legal authority to do so under a valid power of attorney document and was acting on his behalf. (This can raise certain conflict of interest and breach of fiduciary issues depending on the circumstance surrounding any change that was made to the beneficiary designation.)
I would recommend speaking with an attorney as soon as possible, so we can provide more specific advice in your circumstance. You can schedule a free case assessment online at go.oncehub.com/rhbooknow or you can call us at 303-688-0944.