Would they be able to use the light trick? The shell would be prertty hard and thick for this big of an egg if I remember correctly
Your concern is definitely reasonable, but since eggs are porous, it’s easier than you think, even with super tough shells! You can even do the light trick with ostrich eggs, which is the closest to what my harpies lay in size and general shell strength. Eggs generally get their strength from their shape as well, not just how thick the outer layer is.