Is it permissible to set an alarm for Fajr prayer despite heavy sleep and not hearing it, and despite it disturbing one's sibling and preventing them from waking up for prayer, and is one sinful if they do not set it?

Allah has made prayer obligatory at its appointed times, and it is not permissible to delay it except for an excuse such as sleep or combining prayers during travel. Those who delay prayer beyond its time fall under the threat of the noble verse: "So woe to those who pray [But] who are heedless of their prayer." One must take measures to wake up for prayer, and if one delays it due to sleep after having taken these measures, there is no sin. This should be explained gently to the brother, emphasizing that there is no compromise concerning an obligation from Allah. He should be alerted to the prayer if you wake up before him, whether he responds or not.