Your own devices, with a proper backup solution (which you should already have with or without your photos in it). Nobody can mess with your data then.

Personally, I use Syncthing to sync between devices, including a NAS as a target, which regularly backs up to Backblaze.

As a starter, look for a "dumb" service that doesn't treat photos differently from any other type of binary blob. No thumbnails. No grouping by date or location. No tagging other people. The storage service should only concern itself with safekeeping the binaries you upload, not analyzing and processing them. Use your own machine to do the latter.

I stood up a pair of QNAP NAS for both my parents and I, and encrypt-then-backup their photos/documents to my NAS, and vice-versa. RAID 5 or 6 keeps hardware failure at bay, and keeping them tucked away in our respective homes makes fire or flood irrelevent (for this).

QNAP or Asustor has standalone apps my parents can use as well. Without getting your parents involved, you could either pay for remote hosting for your off-site, or trade RAID space with a friend.

I'm using Nextcloud. Works great.

Definitely use client side encryption, if only because it defeats attempts to "repair" image data or rewrite exit headers, etc.

Another good test: upload your photo collection, then download it and binary diff the two sets of files.

Amazon photos is pretty good as a like for like alternative

Managed Nextcloud hosting in the EU is an option.

iCloud

Dropbox, Box, a Microsoft service.

Photoprism