Some of those things can help a little but for the time being you unfortunately must put them in lockdown to avert another attack because the hawk will be back often to acquire another meal. Especially now that it sounds like it has had more than just one meal at your place. (you could possibly give them some fresh air outdoor time while you are directly supervising them, up close, with eye to the sky)
Can you create a covered run somehow, or part of a run? Some folks string netting over their runs or run rope back and forth all over the top so a hawk is reluctant to dive in. If yours free range they're in trouble now that the hawk found them.
I know - it's such a dreadful dilemma.
Flags, CD's, even kites....will work for a while...but they seem to get used to them. The BEST thing to do is keep them in lock down. Out of sight, out of mind. After a few days...the hawk will think they are all gone, and will go look elsewhere for a free meal. Can you put in a covered run for them?? That would be the safest thing for them.