If you suspect a will's signatures have been forged, especially by a family member claiming inheritance, it's crucial to seek expert advice. While private handwriting experts can offer an initial opinion, the definitive verification often comes from government forensic labs, typically involved when police investigate. The most effective legal route is for your mother to challenge the will in civil court, arguing your grandfather died intestate (without a valid will), meaning his property should be divided equally among legal heirs. Consult a local solicitor for guidance on filing a partition suit and the probate process.