If a parent has children in more than one school, they would need to log in to a corresponding parent portal to schedule appointments with teachers from different schools. Alternatively, we can set up a district account that will allow:
admins - to view data of all schools from one district portal;
teacher - to view and schedule (if allowed by the admin) appointments for all schools in the district they work in;
parents - to schedule appointments regarding all children even if they attend different schools in the district.
Note, however, that district accounts are fully compatible with the CSV integration only. With the standalone setup, parents will not be able to create their accounts on the parent portal by themselves.