@larkil,
I think the easiest is to try to have your stakeholders put in the infromation in a sharepoint list instead of excel, because you can run triggers from Sharepoint a lot better than you can from excel, where you have to manually update and have duplicate controls etc, which is a lot harder to do.
Make your list with the relevant information and have people plot it into Sharepoint with all the values, or they can make a flow for themself which does it automatically once they create an event.
So in summary. You need to make two flows:
1. For you (or every) person of your organisation, a flow like the last one I linked which plots the information for every calender created into a sharepoint list.
2. This flow:
Which makes an event in your shared Schools calender once a new item is created in your 'event' list in sharepoint.
Optionally, when you have this working, expand your flow to handle deleting events etc as well, but start with the basics first.
