Below is a simple program which i think has the functionality of what you are asking for. As far as I understand, you have button A on the stage. When you click button A, movie clip B is added to the stage. Movie clip B has button B in it. When you click button B, Movie clip B and button B are removed.
import flash.display.MovieClip;
import flash.display.Sprite;
import flash.events.MouseEvent;
// This creates a movie clip that contains a button.
// This button will remove the movie clip that contains
// it when it is clicked.
var MovieClipB = new MovieClip();
MovieClipB.graphics.lineStyle(1,0);
MovieClipB.graphics.beginFill(0x0000FF,1);
MovieClipB.graphics.drawRect(0,0,50,50);
var ButtonB:MovieClip = new MovieClip();
ButtonB.buttonMode = true;
ButtonB.graphics.lineStyle(1,0);
ButtonB.graphics.beginFill(0xFFFFFF,1)
ButtonB.graphics.drawCircle(0,0,10);
ButtonB.x = ButtonB.y = 25;
MovieClipB.addChild(ButtonB);
ButtonB.addEventListener(MouseEvent.CLICK, removeButtonClickHandler, false, 0, true);
function removeButtonClickHandler(event:MouseEvent):void
{
var button = MovieClip(event.currentTarget);
var container = button.parent;
container.parent.removeChild(container);
}
// This creates a button that starts on the stage.
// When clicked, it adds the movie clip defined above to the stage
var ButtonA:MovieClip = new MovieClip();
ButtonA.buttonMode = true;
ButtonA.graphics.lineStyle(1,0);
ButtonA.graphics.beginFill(0xFF0000,1)
ButtonA.graphics.drawRect(0,0,50,50);
addChild(ButtonA);
ButtonA.x = ButtonA.y = 20;
ButtonA.addEventListener(MouseEvent.CLICK, addButtonClickHandler, false, 0, true);
function addButtonClickHandler(event:MouseEvent) : void
{
addChild(MovieClipB);
MovieClipB.x = 200;
MovieClipB.y = 20;
}