Hello Ayong
It seems there may be a typo in the configuration. The GRE tunnel must terminate on the routers, and in order to do so, the following must be true:
For the configuration in the source device, the IP address command should have the destination IP where the tunnel will terminate on the other device, namely 172.16.12.2. The destination device, should have the same address configured for its ip address command, namely 172.16.12.2. In both cases, the IP address configured was that of the wireshark device, which is incorrect. I will let @ReneMolenaar know to make the correction.
Yes, that is correct. We are not actually explicitly creating tunnel interfaces, that is being done by the mechanism itself, so we must reference the physical interfaces.
I hope this has been helpful!
Laz