It is said that 13-year-old sister and 23-year-old brother have been close and even slept in the same bed because of their good feelings since childhood. Is this normal?

This is not normal. My brother came of age at 23. Adult men are in their prime of life and fully mature physically. Although my sister is 13 years old, she is still a minor, but her physical development has begun to enter adolescence. At this time, it is not appropriate for brother and sister to share a bed. No matter how good the relationship is, we should live separately, not only for safety, but also for everyone's good.