I apologize for my late response and thank you for all of your patience while waiting for a reply. I can definitely understand how frustrating your situation must be, but I wanted to make sure that your issue was addressed. Do you still need help with this issue? I know that there's been a delay in response since you posted.
Please let me know if you need further assistance.
Yes, you can open and view your camera's and devices wherever you go. You do not have to "have" WiFi in both place. An obvious and simple test is to try opening the Google Home app and viewing your devices the next time you drive away from home. You can use the Google Home app over any cellular data.