Can't use second computer

That's how a router works by default. All devices connected to a router will share the same external IP address. The computers should have separate internal or LAN IP addresses. The phones and tablets may have a different external IP depending on how they're configured. For example, if someone has iCloud private relay active, Apple devices like iPhones and iPads will essentially have a VPN active that route traffic through Apple's servers. Even still, they would have the same external IP as the computers with the VPN shut off.

The only way to give one device on your network an external IP is to have the device connected by ethernet to LAN1 on the gateway/router, and then enable bridge mode for that port specifically in the settings on the router. That would also mean that specific device will be isolated from the rest of the home network, so things like file and printer sharing, casting within the home network, etc. will not work on that device. You'd also want to ensure that all security precautions are taken when connecting a PC to a bridged connection since it'll be directly exposed to the outside world. What some users have done is they connected their own router to the bridged LAN port.

Telus also limits external IPs to a maximum of 2 per residential account. Avoid switching devices connected to the bridged LAN port once it's set up or getting a new IP to replace the second one will involve speaking with tech support.