Questions for my novel

I have no idea what would work in a post apocalypse scenario. I also know very little about this hobby.

1. If there was a base setup at the location they are staying at and each of the vehicles had a mobile setup, how far away could they communicate with the base if they were in a suburban/urban environment?

2. Can each vehicle communicate with each other?

3. When dismounted from the vehicles, can they still communicate using handheld radios?

I could use gmrs but I know even less about that. I have more questions but I’d like to get these out of the way first to decide if cb would work in this situation or I should try something else. Or no comms at all.

Thanks.