All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
A man should not sleep in the same bed with his sister if there is no dire need for that. If there is a dire need for it, then it is allowed as long as they are not touching one another and precautions are taken to prevent the exposure of the ‘Awrah (body parts that must be covered as per the Sharee‘ah).
The Hanafi book Haashiyat At-Tahtaawi reads: “It is incumbent to separate in bed between him and his brother, sister, mother, and father because of the relevant Hadeeth of the Prophet . As for sleeping next to each other but with each concealing his/her ‘Awrah with a separate covering, even if there is only one bed cover (in addition to the separate cover mentioned), then there is no objection to that.” [End of quote]
The Shaafi‘i book Haashiyat Ash-Shawbari reads: “Separating them in their beds (in the prophetic narration) may be done in two ways: each child may have his own bed or they sleep in the same bed but separated (by separate covers for each of them), with their bodies not touching one another.” [End of quote]
Allah Knows best.