How did you acclimate them?
Brittle stars are probably the most haridest of the stars...So if they didn't make it, DON'T TRY ANOTHER TYPE!
Bascially the key for stars are acclimation.
Try NOT to expose them to air. Most people say this is ok. But I go with the "Better safe than sorry" method.
A drip Acclimation of 4+HRS is the ONLY METHOD
to acclimate the star. Don't let anyone tell you you can do the float the bag and dump some water deal.
Also you will need a very small heater set to your tanks temp, that you can put in your acclimation bucket as the water temp will drop over the course of 4hrs.
I'd say 4hrs for brittles and 6 hrs for all other stars.
Ophuira can go into more detail as she is resident Brittle star expert.
And also what are you tank Parms? You say they are perfect....perfect for a fish isn't perfect for a Star...