My grandmother created a revocable trust in 1999, naming my mom as trustee. Mom was to get 90% of whatever was left upon grandmother's death, w/ remaining 10% to be split 4 ways among myself, my brother & our 2 cousins. In 3/2012, grandmother changed the trust to my mom being the sole beneficiary and trustee. Grandmother passed in 7/2012 and estate atty. notified myself, brother and cousins that we were no longer beneficiaries and that mom gets everything. My cousins are upset that my mom is the only beneficiary. The letter from the atty. says the trust became irrevocable upon my grandmother's death and no changes can be made. Do the cousins have any legal standing to challenge the trust?