I think(only think, wait for clarification) that switching on the LEDs should be fine. Unfortunately as cuttlegirl has pointed out, the cuttles cannot get the right nutrition from brine, I know you have heard this many times but just bear with the reminder one last time. I think freeze dried should be fine if there is a current that moves the mysis to simulate movement, because cuttlefish mostly rely on eyesight to get their food. If your parents really want you to try using brine, you could refer to the posts here or separate two cuttles and feed one brine and one mysis, though I really wouldn't suggest that.
Good luck!
Good luck!