look first to what the trust document allows. What rights do the beneficiaries have to remove a trustee? What rules are in place for accounting by the trustees and to whom? If the trustees are following all of their duties then it will be difficult to remove them just because the value of the trust is down.
If the trustees are in fact not acting for the exclusive benefit of the beneficiaries or violating their fiduciaray responsibilities then it is possible to ask a court for help to remove them if they won't step down.
If the trust is in fact in a negative status then perhaps the trust really needs to be closed.