Hi Nikhil,
Do you publish activity streams only when the app is in foreground or when the app is in background as well?
If you want to publish activity streams (by sending messages) to users when the app can be either in background or foreground, you can consider using Firebase Cloud Messaging Topic messaging + Firebase Analytics to track the likes and views count.
1a) You can create topic for your "channel", and subscribe users to the right topic. This can be done using client API or server API.
1b) Once users are subscribed to a topic, you can send messages to each topic using server API.
2a) When your user likes or takes an action to view, you can log the event using Analytics
Check out
Firebase Analytics for detail (Under iOS and Android sections, there are the "Log Events" documentation
2b) Once the events are logged, you can view the analytics in the Firebase Console Analytics tab. Look for the event name that you have logged under "Events" tab
Hope this helps!