AS2 - addressing btns in an attached movie clip

I have a series of mc’s I’m attaching from the library, with buttons in the main movie. Inside each of the attached mc’s is a close button that needs to close the attached mc and launch a function in the main movie, but I’m having trouble addressing the button inside the attached mc from the main timeline.

I’ve tried this:

calloutHolder_mc.attachMovie("mar01callout", "callout_mc", 0);

calloutHolder_mc.callout_mc.close_btn.onRelease = function(){
    this._yscale = 0;
    new Tween(greyGrids_mc, "_alpha", Strong.easeInOut, 100, 0, 1, true);
    new Tween(dayColorBar_mc, "_yscale", Strong.easeInOut, 100, 0, 1, true);

but I’m unable to write any version of this on the main timeline that allows me to communicate with that close button.

It’s also a problem because in some of the attached mc’s there are additional buttons that have other uses and I’ll need to communicate with them as well.