Newly hatched queen caterpillars are cannibalistic if they find other queen or monarch eggs.  The best thing to do when your live female lays more than one egg (this is often the case) is to cut away the egg and place it individually into a small plastic container, like a solo or sweetheart cup, and wait for it to hatch.  Then place it on fresh cuttings of milkweed in your rearing cage or bucket.