In CASES21, when entering new student data there's a section to add notes for contacting parents.
There should be a note section on a student's profile next to their parents contact information to let staff know when parents can be contacted.
Also wanted to add that only certain staff can see access restrictions. There should be a brief note without going into detail for all staff (e.g. Do not contact Dad or split custody household contact Mum every M-W)
If parent availability changes, they can contact the school