I don’t think Joplin does real-time collaboration, if that is the kind of collaboration you’re looking for. If you don’t expect you and your wife to edit documents at the same time, it may work for you. For me, I almost exclusively want to real-time edit lists with my partner.
My current system gets around real-time collaboration needs by using 3 obsidian notes in a shared obsidian vault. For example, my partner and I each have a grocery list with a dataview showing the other’s list in their own. That way my partner can edit their list and I can see what they’re editing while doing the same on mine, thus avoiding collisions. Then, I have an in-store grocery list view that joins the two lists and groups by isle, and we just check off things on a single phone as we put them in the cart.
I would LOVE to get away from this system.
Hedgedoc 2.0 will have an Explore Page when it comes out, and with that, I think it will solve my use case. It has a good-enough mobile interface, and markdown isn’t terrible.
For the music festival, have you considered something more robust like a wiki?