Hi, thanks for your question. Please confirm again what your mother's will states as you have said she has left 75% of her estate to you and 25% to your mother, a chair to your brother and the rest of the estate to you - which is unclear exactly what she has bequeathed.
Thank you for your question
My name is ***** ***** I shall do my best to help you.
Since your Aunt dies before your mother then her money goes into your mother's Estate and is distributed between you and your brother in accordance with the term's of your mother's Will.
Accordingly your brother will receive 25%
Please ask if you need further details