In-App Chat Capability

I’m currently building a product for police workforce for task management. In-app chat would be one of the feature in this app so they can coordinate with each other regarding their task.

They’re used to using WhatsApp as their communication tool, but my company would like them to shift into our app completely. Should we implement an in-app chat as advance as WhatsApp or would that cause a problem (eg: app crashing because it’s too heavy)? Would copying other messengers features benefit us in trying to shift their chatting platform? Or is it better to just implement a simple in-app chat feature like Twitter/Instagram and not try to replace their current platform?