Sorry to hear :( There's nothing much to say except hope the remaining survive.
Any treatment to be done in the DT involves you removing all inverts and corals -- once you remove them, you can treat with hyposalinity for a few weeks, then gradually bring the salinity back up. If you lower it too slow, the ich will adapt. If you lower too fast, the alread-stressed fish could die. Others have gotten rid of ich sucessfully this way. AGAIN, remove all corals and inverts.
The other way is harsher -- catch all the fish, treat them with copper in a QT (you can also just go hypo in the qt instead of the dt). The problem is putting them back in the dt will give them ich again. You'd have to leave your tank fallow for 6-8 weeks. Inverts and corals are not affected by ich.
BTW -- just cuz they show no signs of ich doesn't mean they do not have it. They're just handling it better. To be honest, you can leave ich alone and let the fish fight it on their own, which over time, will make them more resistant to ich as their bodies learn to fight it. Drawback is you never know if they'll survive or not.