here’s a list of caldav providers: CalDAV · Tasks - fruux is nice, but at the family pricing you can already look into hosted nextcloud (hetzner specifically) where you have unlimited users.
Editing each others calendars is hard (write access), just subscribing is easy.
One advice is if the use-case is family calendar with no secrets and everybody contributing: create a separate user account that every device has access to as basis to do “common calendars”