Islam teaches us to safeguard ourselves against temptations by avoiding, to the best of our ability, all circumstances that may inadvertently lead to them. Therefore, it is not at all advisable for a Muslim brother and sister to sleep in the same room, in order not to make themselves vulnerable to Satanic suggestions and temptations.
Sheikh Ahmad Kutty, a senior lecturer and Islamic scholar at the Islamic Institute of Toronto, Ontario, Canada, states:
It is not at all advisable for a Muslim brother and sister to sleep in the same room, for by doing so, they are unnecessarily making themselves vulnerable to Satanic suggestions and temptations. Islam teaches us to safeguard ourselves against temptations by avoiding, to the best of our ability, all circumstances that may inadvertently lead to them. The Prophet (peace and blessings be upon him) said, “The Devil runs through the blood-veins of sons of Adam.” Let us never forget the Qur’anic teaching that Satan is our sworn enemy who is ever determined to waylay us in order to drag us into perdition by casting evil suggestions in our minds. He does so by exploiting our most vulnerable moments.
Therefore, it is imperative that we always act vigilantly. How often do we hear of people in similar situations falling prey to the evil suggestions of the evil one, thus dragging themselves into perdition?
So I must advise against sharing the same room between matured siblings. The Prophet (peace and blessings be upon him) ordered parents “to separate them in sleeping arrangement when they reach the age of ten.” This can be taken to mean different rooms, especially if they are all by themselves.