I guess I could set up tailscale or some other vpn access to my network but I don’t feel like explaining that to parents and siblings.

Just set up VPN between your router and their router, no need to explain anything.

What is this ‘offline’ thing I keep hearing about?

So no useful features for me.

I don’t want to share my media with anyone and see no reason to stream from outside my house, it’s not like I can take my home cinema with me. Also, why would you want to re-encode and lower the quality?

Plex works just fine without a subscription. What is the subscription even for?