That's so funny that you have an expected hatch date of 8/16, because my first ever four leo eggies are expected on the same date. From what I've read, they can be housed together until they're old enough to be sexed, so you can separate males (to keep them from fighting) or earlier if you see some babies being aggressive. I believe you can feed small mealworms from day one. Calcium is fine. I was actually gonna put some calcium and vitamin powder on my finger and get them to lick it a couple times; I do this with my females occasionally just because I wanna make sure they're getting plenty. I also put vitamin powder on my mealworms prior to feeding.

All I know about slimming down is that those females are PIGLETS! I hardly ever see my males get to eat unless I feed crickets. If that doesn't slim him down I don't know what will