Atomic bombers help!

So this is my first time doing Nukes and I’ve got several atomic bombers ready to use. The enemy has a massive stack of troops with roughly 4k hp with no AA or interceptors defending. Is it best to single fire my atomic bombers and see the damage after each single blast or send 3-4 at a time? Does the damage stack? And can other bombers get into the fallout zone after the first bombs goes off?