Seahorse fry especially need a nursery tank. There have been a few cases of kuda, etc. being raised in a large, macro filled tank- but I can't remember the link. And yes, reidi are harder to raise- some of the smallest fry from what i've heard. I had a chance to raise 10 baby reidi, they only lasted 5 days (it was a random act) though. I've never seen any other fry in person, so I can't personally comment on size issues compared to other species.
Good luck with them! Just make sure they don't snick air, etc. and get some baby brine shrimp and possibly rotifers going if you'd like to raise them.