Generally, the Separation Agreement, if properly prepared by a competent attorney, will include a provision stating that neither party will have any claim to the estate of the other party despite any Will. Please check the Separation Agreement.
Any judge who reviews such a claim by a separated husband should be skeptical and should require additional investigation about the matter. It may be helpful for you to contact the lawyer who drew up the will or a lawyer with whom your sister may have consulted who may have further information, or have a copy of the latest will.
Leonard M. Weiner, Esq./DivorceSolutions