Q 1: Is it permissible to believe those who
claim that their souls have the ability to speak to the dead in their graves during their sleep?
They claim it is out of their hands and is done with Allah's Power.
Those people are liar charlatans who manipulate people's minds. It is not permissible to believe them or resort to them. Rather, you should deny their actions, warn people against them and report them to the authorities to punish them and save people from their evil.May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.