The diet could be improved simply be eliminating the scratch and slowing down on the treats. Other than that, diet isn't likely the huge issue here.
You have 18 hens older than 24 weeks, right? However, only two are laying. It could be the others just need more time, but also, since you are apparently bringing home chickens from a sale that you are likely importing lots of funkiness by way diseases and parasites as well. Worming was a good idea. Do you have to repeat the treatment so many times? Most folks do a 30 day total separation of new chickens for health reasons.
Don't forget to add a little light in the am, if you wish to help them in that regard. Watch for egg eaters. Not likely, but thought I'd mention it. Also be sure you don't let them roam. Keep them in the coop/run until this is all resolved. You don't want/need to go on an egg hunt for secret nests.