AITA for skipping my brother's wedding because his fiancée excluded my wife from the guest list?

What should have been a joyous family celebration turns into a heartbreaking dilemma when Mark's fiancée, Alice, refuses to invite his brother’s wife, Amy, to their wedding. Tensions rise as past grievances resurface, and Mark insists that his brother attend alone "for the sake of family harmony." Caught between loyalty to his wife and love for his only sibling, he must decide whether to keep the peace or stand up for what’s right-risking permanent damage to his family relationships. As emotions run high, one question remains: is unity worth the price of betrayal?