Use another Macbook Pro with touchbar as secondary screen
You can only use iMac as a secondary screen with Mini DisplayPort to Mini DisplayPort. Target Display Mode lets you use the built-in display on a supported iMac as an external display for another Mac. To use your iMac as a display in Target Display Mode, connect it to another Mac using the correct cable (see System Requirements below). 



However,

Connecting two MBPros to create an extended screen won't work. Use VNC viewer as Remote Desktop if you want else I don't see any option as I am daily working on Apple devices and people has come up with this request many time.