If they’re not technical and you don’t feel like playing family help desk, you can’t go wrong with either synology or qnap. The downside with them is the hardware is just barely powerful enough for a NAS. If they start to get into self-hosting at all – pihole, home-assistant, minecraft servers, jellyfin, etc – they’ll quickly run into limitations.
If they’re somewhat technical but not a Linux guru, I’d add Unraid (slackware based, but 100% UI-driven) to the list. I’ve been running it for years and it’s been great. It makes running docker/VM a breeze on top of the hardware-agnostic setup of mixed drives that makes upgrading slowly over time painless.
A Shield TV is probably overkill for you and the recommendations of a pi would do just fine, but if it’s in budget I say go for the Shield TV. Mine is nearly 8 years old and I haven’t had a single issue, streams 4k HDR, and runs so much better than any of the crap that comes with even the newest of TVs.