Certainly it is possible (the app would be complex) What have YOU tried?
What type of geofence? Users use circular geofences, rectangular geofences and / or calculate distance to a coordinates to determine whether a device is within a particular geofence. See Search results for 'geofence' - MIT App Inventor Community which has 23 discussions about the topic. Take your pick.
Use a Clock and a CloudDB or FirebaseDB or a spreadscheet as a database to post when entered the geofence and when exited. Use the Math blocks and Clock to determine duration within the geofence.
Examples of tracking multiple users (but not all the things you hope to achieve):
