Life Insurance

I doubt it, although I'd have to review all of the paperwork to be certain.  If the policy is in an irrevocable trust, your step mother probably doesn't have the ability to change the beneficiaries.  Depending on how the trust is worded, your brother might not have the power to refuse to pay you your share of the policy.  And the agreement, if it's in writing, separate from the trust document itself, might also have something to say about this.

There probably isn't anything to be done here, though, as long as your step mother is still alive.  Please talk to a local attorney, who can discuss all of the facts and look at the papers, for reliable advice.