Thank you all for your input.
I'm looking into #grocy
right now. It has way more features than is needed but I might be able to remove them for the users to keep it simple and clean. The calendar view is great.
I didn't know about #taskwarrior
. That is exactly what I would use. Not my family though. I'm showing it off to some colleagues and the project might have some new users in the future.
For file sharing we use #seafile
instead of #nextcloud
because of E2E encryption without storing keys at the server. I still have an old version running somewhere for testing purposes. I have a look at the #carnet