How can a Muslim woman achieve salvation and endure the harm inflicted by her mother who is trying to Christianize family members, and the harm from her gloating sister due to the grandmother's will?

The sister should bear in mind that life is a place of trial, and that patience in the face of tribulation atones for sins and raises one's rank. She should also recall the biographies of the prophets and the righteous who endured harm with patience, and she should strive to associate with righteous sisters. It is important to acquire religious knowledge to protect herself and her family from poisonous ideas. She can threaten the grandmother and sister with reporting the matter to the authorities and filing a complaint if necessary, especially since there are death threats.