If you need multiplayer sync, I've been working on a plugin that makes Obsidian real-time multiplayer (like google docs) called Relay [0]. A lot of our users use it in combination with SyncThing to keep it entirely free for up to 3 users (we also offer a paid plan with attachment storage and more seats).
[0] https://relay.md
I'd recommend you to look into SyncThing Fork or a similar tool if you never want your notes to leave your own server.
I wrote about ways to sync Obsidian here: https://bryanhogan.com/blog/how-to-sync-obsidian