It’s worth noting that there are two ways to use Joplin for to-dos: you can embed a complete list within a note, or make a bunch of ‘todo-able’ notes in a folder that can be individually checked off as completed from the note list itself. I’d usually say the advantage to using separate notes is that each note can have its own content within the body of the note, but with your use case of shared list syncing between people you’re also less likely to end up with conflicts if people aren’t editing one large note, since Joplin isn’t a platform that sends all the connected clients updates in real-time.