Can my brother, who is trustee of my mother’s Trust, control my activities when I visit her and prevent me from seeing Trust and other documents?

1) Having control over a trust has *nothing* to do with your mother's person or your visits to her: he would have no control over what you do when you visit your mother unless she is mentally incompetent and he has been appointed her legal guardian.
2) You are an interested party, as a child of your mother, especially if you are in any way of a beneficiary of her trust; even if you are not a beneficiary of the trust, you have  general interest in her estate (and so in her money/assets), as a potential heir and also, as a child, would potentially have standing to make sure that her trustee (your brother) is not taking advantage of her. If there is any reasonable question about her mental capacity or his control over her, you should be able to bring a legal action (lawsuit) in chancery court to see the documents and/or get an accounting of his actions as trustee, but such an action is complex and could also involve a hearing into her mental capacity. You are advised to consult with an elder law attorney about the situation.
Note that if you mother is mentally competent and there's no reasonable grounds to feel that your brother is exerting undue or improper control over her (for example, improper control or undue influence can be found if she is housebound physically and he controls her access to the outside world; but if is mobile and active and gets out, that's not a factor), then she has the right to simply tell that this is "none of your business"--one adult, even a child, cannot interfere in another competent adult's affairs unless there is something untoward going on.