Clan Wars: online (Autumn 2008)

I don't understand anything! My clan leader messaged me on ICQ, asking on behalf of the general if I could play for Fortress. I replied that I could try, but only if I could also play for the clan at the same time. They said I could. Then I thought about it and realized that this is nonsense! What if, for example, we are in the same group as Fortress? Would I be a double agent? I think, I'm not sure if the same situation applies to Smok! So, please, can someone explain something to me? :)