What can I do against suspicious will claiming grandmother’s property?

My mother and her sister (my aunt) were the only two daughters of my maternal grandparents. My aunt was separated from her husband and lived with my grandmother. Her son's custody was with the father, and there was no contact between them. After my grandmother’s death, a will—allegedly made fraudulently—states that the property would go to my aunt, and after her, it would be divided between both daughters' sons. However, since my aunt had no relationship with her son and he never took care of her or my grandparents, we do not agree that he should inherit any share. We believe the will is suspicious and want legal guidance.