When composing a new group message you can select two options: Individual and Group (MMS), and it will remember your choice, so if you want to switch back, go to the "Messaging" settings in Truecaller and tap on "Send message to group as"...
How it works!
1) Individual: The SMS will be sent to each and every selected recipient separately (separate threads).
2) Group (MMS): It will create a group thread and everyone in that group can see the people you included and the content. When someone in that group replies directly from the group thread, all participants will see the SMS but in a separate thread.
What happens if someone replies back to the separate thread?
Answer: Only you will get that reply. They need to reply in the first group thread in order for everyone to see the message.
We're currently developing a group chat feature for our new feature Truecaller Chat which won't create separate threads since it goes through the internet while SMS is a regular carrier plan.
Hope this explains a bit more. For any questions, please tap here.