We all have a share of two homes. My mother has part of the ownership as long as alive. Can we just say we are selling the house, even if the other part owner doesn't?

Is the house in trust or are you saying that
Your mother has a life estate and you and your siblings have undivided interests in the remainder?

If the former, the trustee can sell the house if allowed by the terms of the trust.

If the latter, the remainder interest in the house can be sold subject to your mother's life estate. Thus the buyers could only take possession upon her death. You cannot sell her life estate.