"Vulnerable patient"

My extremely vulnerable brother who often displays challenging behaviour has been admitted to ward 4. As he needs constant supervision, my mother has been sitting with him throughout the day. Apparently, this unique set of needs don't require supervision at night and she has been told to leave. As he often has interrupted nights, this exposes him to strangers managing him which will undoubtedly exacerbate any behavioural issues and cause undue distress. I appreciate that we are in COVID times but this would result in increased pressure for staff, who neither understand his behaviour, or have the relevant skills to deal with him. Why is supervision acknowledged as a requirement during the day but not at night? After all this is an increased time of risk for all staff and patients. I am extremely unhappy with this lack of understanding in an extremely challenging time, would you let a child stay overnight without a parent? As this is the level of capacity my brother has!