Since you mention stuff like "the video isn't important", "other services" (plural), I'd consider not just one alternative but several. The big problem with big name social media is that they provide a all-in-one experience that is designed for profit, and as such looks and acts worse than any of its independent parts (not to mention, the sum is artificially made more addictive to users).
- For publishing campaign materials itself, all you need is a filehost or filebin - something like pastebin.com but that allows you to upload and organize any kind of files. Any of the offerings in the FOSS market will do, but if you are going to focus on posting quickie (rich¡) text documents that are easy to build and parse I'd suggest a Markdown-based document bin like Hedgedoc.
- If your campaign is gonna run like a chat, XMPP / Jabber. There's servers like Prosody or ejabberd that are easy to set up.
- If your campaign is gonna run in web "play by post" mode, any modern web forum system will do, for example Discourse. Heck, even oldie-style web forums might do, like phpBB.
- Voice: Jabber has access to audio IIRC. I've also heard very good things about Mumble.
"Our failure".
Signal worked perfectly here: if you add a contact, they get the messages.
What failed was the Trumpist, like at everything else.