Usually you get on his Android smartphone more WhatsApp messages as SMS messages. Therefore, it is perhaps important for one or the other of you to disable the vibration for incoming messages only for WhatsApp.
That is why we tell you here's how you can disable only the vibration for incoming WhatsApp messages.
Opens this on the Android smartphone app "WhatsApp" and typed there then in the overview on the top-right three-point symbol. In the pop-up menu, select "Settings". From here it then goes on "Notifications" -> "Vibration duration".
So you see a window with different information:
out
standard
short
long
Select here now "Off" to completely disable vibration in WhatsApp. Finished!
Immediately your Android smartphone is no longer vibrate with the input of a WhatsApp message.