You can use a stream for all the profile picture of the participants in the chatroom. I don’t know how exactly is your database structured but what you can do is do something like this everytime someone updates his profile picture:

1. Update his profile picture on users/ collection.
2. Use a Firebase cloud function to update his profile picture asynchronously on all the chats he is part of (this means that you’ll maintain a map of username:profilepicture for all the participants in the chat).