Is it permissible for me to be the primary beneficiary of my non-Muslim brother's bank funds after his death?

A will made by a non-Muslim in favor of a Muslim is permissible, because disbelief does not negate the capacity for ownership. Just as his sales and gifts are valid, so too is his will. Therefore, it is not permissible for the Muslim to take more than one-third of the inheritance if the non-Muslim has other heirs, unless they agree. However, if he has no heirs, the Muslim is entitled to take all the bequeathed wealth.