One device has my Sim card, the other one only the internet connection. Both devices have already been verified by my number. Will I get incoming messagges in both devices?
You're not allowed to do this, From whatsapp FAQ:
Using one WhatsApp account on multiple phones, or with multiple phone numbers Your WhatsApp account can only be verified with one number on one device. If you have a dual SIM phone, please note that you still must choose one number to verify with WhatsApp. There is no option to have a WhatsApp account with two phone numbers.
If you attempt to frequently switch your WhatsApp account between different devices, at a certain point, you may be blocked from re-verifying your account. Please don't repeatedly switch between different devices and numbers.
You cannot use the same WhatsApp account on more than one device at a time. As soon as you sign-in to a new device, the old one becomes invalidated. WhatsApp does not support a 2nd device.