Thank you. Yes, you can click each one only once per turn. If you want to hit it multiple times (or with a higher number), you have wait for the next turn and/or try to approaches from a more fitting neighbor or let it explode from them.
I know, rules are a bit complex at the beginning (have to think about make them easier to understand), but as soon as you got them, there are actually different strategies (but i by myself am also still not fully aware, which one is the best, even after playing 100s of rounds during development ^^)