One calendar the whole clan can write on.
Every year as a family we bought buy a paper "family" calendar.
One of those ones that has 5 columns. Enough columns for each member of
our clan, and an extra one.
A monthly calendar that allows us to mark events, activities, holidays and more to a family member, or the "family" column (remember that extra column).
This has worked wonders for a number of years—until it hasn't.
The calendar on a wall is only ever in one place. It doesn't come to work with you, or to the school gates, being able to see what's on when not at home becomes an annoyance.