Give each entry an owner
Clarify who handles an appointment or preparation task as well as when it happens. Note location, time and the next step without unnecessary detail. Do not assume everyone checks a calendar equally often; agree how updates will be communicated.
Review sharing permissions
Check who can open the calendar link and who can change entries. Keep health documents out of public description fields. Disable an old sharing link in the relevant app when it is no longer needed.
Your next little step
Choose one idea that suits your family and try it at your own pace. Every family has different needs.