Yeah, true. I think there's no way around being pushy/almost manipulative.
"I fortunately no longer have WhatsApp. Especially with things concerning our children, I would NOT trust Facebook with that. I am completely open to using something else, does not have to be Signal - do you use any secure and private messenger apps where we can create a group?"
It's an uphill battle for sure. And you have to think about and set your own limits. I hate using WA, but for some contacts, it's better than having NO contact.
What are you talking about. Please clarify if this is actually true:
This would mean that you only want to access Jellyfin when you, and the device you are watching your show/movie on, are at home, where the Pi/server also is.
Is this correct?
If so, then questions about VPN, Certificates, DNS,.... do not matter.
Now you can access it at home, and only at home. I honestly fail to see where a VPN would even come into the equation here (again, if you wish to ONLY watch when you are at home, as you've said).