Can I get out of the irrevoccable trust with my 3 siblings who will not sign off? What are the odds of winning in court?

I don't practice in NY so take this for what it's worth.  In order to determine your rights, you must review the Trust document itself.  Does it give you the right to separate your share from your other siblings and perhaps have it managed separately but still in trust?  Does it give you the right to terminate the trust and for you to take distribution of your share?  No one can answer your question without reviewing the trust document.  What's the dispute?  Do you just need the money or is there mismanagement?  Mismanagement can be addressed w/o breaking the trust.  Maybe you can even replace the trustee -- most states read into the trust the ability of the beneficiaries to replace the trustee.  It's usually a tough battle unless you can get all other interested parties on board with a plan.