I use obsidian and syncthing, although I use it for just myself; as long as you aren’t editing the same document at once it should work. If there is a file conflict, nothing will be deleted, just the conflicted file with have the word “conflict” in the name. So you can do a text compare between the original and that file to see what needs to be merged.

Syncthing is self hosted, obsidian has desktop and android apps. You can exclude certain files or folders from being synced on a certain device with syncthing. Obsidian uses markdown so that might take some getting used to, but the plus side being all your notes will be text so you aren’t locked in to using obsidian.

You can also use another markdown / text editor as well, maybe one that supports wiki links for obsidian compatibility but obsidian works with the markdown link format as well.