Congratulations. I remember a similar celebration in my life too. I have lived nearly 15 years longer than my mother. I truly celebrated my 50, not as over any hill but a celebration of reaching the hill. I do miss not having her advise about her years from 49 on but I make sure to pass the day by day trials and joys of life on to my children. (Many more joys than trials.)
Celebrate to day wildly and enjoy every birthday forward from here. You are carrying on the legacy of your mother and brother. What a gift you have to give on their behalf!