They will not hatch at the same time, but eggs from the same clutch will all hatch within 1-2 weeks of each other. If they are sepia Bandnensis, they 'should' not eat each other. I emphasize should because at one time a couple years ago, some eggs sold as bandensis circulated to a few hobbyists where these babies were very cannibalistic. In every other experience Ive had or heard of, cannibalism does not occur.
I have been resarching how to care for cuttle fish in captivity for three years, and was wondering if anyone could tell me if they think I am ready to give one a shot. Please don't be afraid to say no. And in the event that I start a cuttle tank I am planning on using a 55 gallon and was going to stalk it with 4 cuttles.