family secretiveness becoming a major life problem...?

I have two other siblings one lives in nj and lives close to my mom who lives in a assisted living facility. My sister lives in florida, and makes trips to nj a few times a year. My siblings and i have decided to put together a trust for my mom. however, my siblings, basically dictated to me that i can't discuss the trust with my husband, and the reasoning is that my sister didn't tell her husband, therefore, I can't tell mine. In addition, every time, I go to talk to my siblings about the trust on the phone, my sister always, and I mean always asks me, " if I am alone in the room" so my husband/ kids won't hear.Now it is time for us to sign the trust, but I need to read the final copy. however my siblings don't want any copies sent to my home or my sisters home. I can't read the final copy before signing it. My self and my husband always look over all the documents that we sign no matter what. But my siblings, are adamant about my no one knowing anything. I live in california so it not so easy for me to hop on a plane and sign documents. I don't know when I can get there any time soon. I believe they don;t want my husband to know because he and my sister got into a huge fight over 5 years ago and she never moved on, she still holds a grudge over something so petty and stupid. Plus my sister has a big ego and my brother is a bully. I am stuck in the middle and I don't know how to handle signing this trust documents.