I totally understand where you are coming from. My father, whom I adored, died when I was ten. Three months later our mother left us with my Dad's mother and she came up with ways to abuse and embaress and terrify us every day. The razor strap was her favorite and if we had committed some infraction of the rules, she would wake us up by using it.

When I was 18, I left, and because of her lies, the entire family cut me out of their life. I never questioed their motivations. I knew she was crazy, in a really bad way. So when I left, I left for good and have never tried to contact any of them again. I have no regrets and have never looked back.

My point here, is that when someone hurts you on a continual basis, it is time to get away from them. If your brother is causing you so much pain, perhaps it would be best to take a break from your relationship with him.
As for your Mom, please stop feeling so guilty. It was never about you, it was the meaness and sickess and jealousy in her heart that made her the way she was. The reading of the will thing is one of the cruelest things I've ever heard of.

It seems that you are trying to find excuses for their behavior, when their really isn't one. Some people are just flat out hateful and bitter. And since they have never taken responsibility for their own failures, they must find a scapgoat to take it out on.

I'm happy that you had a good father and sorry he is gone. But hang onto that and realize the way he treated you was the way you deserved to be treated. Cherish his memory and maybe write him a letter now and then.

Let them wallow in their own unhappiness. And maybe by making them part of your past, you will find your own happiness.