A good old NAS, mounted into the filesystem, because the UI/UX is well-known and anything else than that is confusing for my family.

I just made them install Tailscale (because internet-facing NAS was getting attacked/probed all the time), and I configured the ACLs on my end so they could see the NAS’ at its ts.net address.

Nextcloud has matured given its support in Germany; Hetzner will even rent you a Nextcloud box- works for me. https://www.hetzner.com/storage/storage-share/ Sharing of folders containing documents or photos or whatever works fine. Can share family recipes, shared costs for holidays. Also works as password manager, bookmarks manager and other things

A tiny VM with the disk space to fit your needs using only OpenSSH + NGinx with autoindex enabled should suffice. Enable basic authentication on NGinx. Upload files via SFTP. Directories for your documents, tax records, photos, to-do lists. That's pretty much it. If family members need to upload files there are SFTP clients with a UI. Simple instructions with screenshots should suffice to get them going.

If you are not behind CG-NAT this can also be done from your home connection if it has the speed required to meet your family needs.

The photos/tax folder is write/read only? (i.e. not delete nor rewrite?)