Can I trigger events to happen in my game / app live

So say I have an app with multiple people in the immediate vicinity with the app on their devices, is it possible to send triggers / events live so that the same thing happens at the same time on each of the users device? This would not need to work over larger distances as all users would be in the same room and if necessary connected to the same wi-fi.

You are talking about full multiplayer features.
Using unity network you can make everyone that is using the same wifi connect automatically to the same “room”. I don’t believe this is proper way to do this, but it is a quick way for you to test the concept.
For this to work with GPS, you will need a lot more things like a custom server to check who is closer,…