If Game Master mode is enabled in parties, there should be a mode added that allows everyone to view/pan/walk around (depending on the gamemode) and use the chat feature and/or collaborate in call to coordinate the country that everyone thinks it is. At the Game Master's discretion, they would then pick the country as if it were singleplayer country streaks.

Currently, if I want to country streak with my friends, we have to send individual challenge links to each other, and I believe that a solution like this would be much more enjoyable for everyone