Since the messages are not publicly announced by the apps themselves you would need to capture the network traffic & try to read the information out of there. But it might be impossible if the apps transfer their messages encrypted (https etc).
Packetcapture either requires root & tcpdump
(or similar) on the device or Android 4+ and a VPN service like done in tPacketCapture
I don't believe that packet capture via VPN service is intended to be possible so that might be blocked again in future versions of Android.
How do I capture instant message traffic on an Android?
So basically you can't do that in a standard app unless the messenger apps provide an API to do so.