Alliance attack coordination

Is it possible to synchronise attacks between members of my alliance? Or do I just have to tell my buddies the time to land their attacks? Will they be able to see my troops attacking as well as their own if they land at the same time? I know how to synchronise attacks between my own castles.

Members of your Alianz can‘t see your forces.
You have to Tell them, When they have attack.
-I Hope I can help