Hi, looking for help for my mother

[Notlaw]

My stepfather recently died, and according to my mother has left a significant amount of money in his estate. They had been married for forty years, but he made his will a few years ago without my mother's knowledge. It is only now that my mother has discovered she is to be left only 10% of the estate, with the remainder going to my stepfather's children. In the past they had lived a reasonable retirement, foreign holidays, new cars every few years etc. What has been left to my mother will see her living a much less reasonable retirement especially should she require care in the next few years. I am told that my stepfather told his advisor who was drawing up the will that he was leaving 10% to my mother since she would continue to receive a portion of his pension and that she owned outright the house they lived in, so 10% was adequate. I am very concerned for mother and would welcome any advice at to how we might proceed.