your code is doing exactly what you describe and what you should expect it to do. what is it you want your code to do?
When ROLL_OVER btn3_mc I want it to add rooster_mc to the top of btn3_mc (which it is doing), but btn3_mc and rooster_mc start flickering wildly. I want to stop that. And when I ROLL_OVER btn_mc I want to play flowers_mc (which it is doing), but it appears to be calling flowers_mc multiple times with no real consistency. I want to just have it come up once at a time.
you need to rethink your coding.
when you rollover btn3_mc and add an object the triggers a rollout event (which is what happens when you add rooster_mc above your button) and then your rollout triggers a rollover (which what happens when you remove rooster_mc), you're causing a loop and the resultant rooster_mc flickering.
and your btn_mc rollover triggers a new flowers_mc with each rollover. if you don't want that to occur, don't encode that.