Happy to see the Cooperative Quests! Should be fun. One suggestion - might help to have the neighbor's name at the top of the Quest window. I was going along my neighbor bar checking all of them and I kept forgetting where I was.
Also, one neighbor had the blue "Collect Coins" thing. Since it was blue, it made me think I could collect some coins, too, but I clicked it and nothing happened. If we're supposed to get coins, mine didn't work. If we're not, maybe that button shouldn't be visible to non-owners? Or shouldn't be blue?
Anyway . . . just thoughts. So far, so good! I got probably 8 - 10 things I needed just in one round through my neighbors and a lot of neighbors hadn't started quests yet. Should be even better as more people play.
Thanks, devs!