I had an idea for the alliance halls.
Because of how much trouble it would cause to have joint ownership, when guilds leave the alliance, I think one guild has to be put as owner of the alliance hall.
Think of it like this:
One guild starts and alliance and is now the alliance leader. They then recruit other guilds to fill in the officer, elder member, member, and recruit positions. When building the alliance hall, it is the leader guild that queues the upgrades. Other members of the alliance donate the fund/materials to build the hall, but in the end the leading guild owns it. That way people understand where things are going when they put effort into an alliance’s hall and if they leave they know they won’t be taking anything with them. If the leading guild decides to leave the alliance, they pass the leadership and ownership of the guild hall on to another guild within the alliance.