Maybe, the lower temp might help them it will certainly slow down the use of the yolk sac.
It's hard, it's not great when they don't develop but at the same time there is very little you can do at that stage. All of the development up to the point of first feeding is controlled by the environment (temp usually) and the nutrients contained within the eggs. so they best thing to do is try and influence it on the broodstock end and accept that even with 30 years of international investigation (and Literally Billions of £'s) behind doing this in aquaculture the best results for this stage for some species can still be as low at 20-30% survival. Edit: And that is after maybe 30% loss at hatch. so you are looking at the end result after weaning (going from live to pellets) at less than 10% of fertilised eggs surviving.
I don't know, I have never used them. The main ones for Aquaculture are Brine shrimp, Copepods and Rotifers. I would guess that if they are quite small they probably will be ok