Who will be included in the family agreement at my mother's death

I was unaware my sister obtained Power of Attorney when my mother was diagnosed with cancer. I found by accident my sister had put herself on all of Mama's bank accounts make them hers at Mama's death. On Mama's investments she gave herself 90% beneficiary and by brother and myself were to get 10% to share. Mama had to sue my sister to get control back. Mama still being very ill could not take care of her finances. I didn't trust my sister and my sister didn't trust me. Thus a bank was appointed limited guardianship. We have a legal family agreement for us 3 children to have all divided equally among us after $86000.00 is taken off the top for my brother and myself each. My brother has passed away a year ago and Mama is still alive. He has no children.Will his wife now get my brother's even though my Mother was still alive when he died? This is not a will but a family agreement. Mama's real estate is not in this agreement, only her finances.