What. The. Hell. Depending on the jurisdiction, the brother could contest the will. In Canada, a will can be overruled if it contravenes Section 15 (Equality Rights) of the Canadian Charter of Rights and Freedoms. Wills have to be written in accordance with public policy.

LW not only risks severing his relationship with their brother, they also risk severing their relationship with his sister too. They need to think very carefully about that if they decide to keep the money.