If someone books one tour, are my other tours still bookable at that time?

No. A confirmed booking closes those hours on every tour you run, not just the one that was booked, with a turnaround gap either side so you are not expected to finish in one place and start in another at the same minute.

This is on by default and you do not have to do anything for it. If you work with other guides and want your tours bookable at the same time, you can turn off Only book me for one tour at a time in your guide profile, where you can also set how long the gap between tours should be.