Your message caught my attention... I am sorry to hear about your loss and struggles.

Perspective matters, here is my life story for you. Imagine you are in a hurry driving to get to your destination. Someone in front of you is going really slow and you can't get around them... they won't let you. They block you so you honk your horn and/or show your frustration to them to let them know you are in a hurry, but it just escalates.
Once you acknowledge they have control over you, because that is what they are doing by blocking you, most people will continue to hold onto that control.

Better to back off and act as if their actions don't bother you. If they aren't controlling you they will lose that focus and will leave you an opening to get around them.

You obviously smart, articulate yourself well and have a caring heart.

Once you back off with your brother and accept him without expectation, you and your brother just might find a way to celebrate your mother's life together💗