I think someone has cursed my coop! J/k.......but seriously, please help!

Ok, I will try to make this the least confusing I can. On August 5th, we got 6 hen pullets from someone we found on local classifieds. He said they were 5mos old, and I have no reason to think he was incorrect; they seemed small and juvenile, since then they've molted, filled out, gotten taller and have turned into lovely, fluffy, shiny chickens. They have a coop and yard, (obviously) we feed them pellets, (just keep the pan full-ish) scratch grains, and they have free access to calcium. We also open their gate and let them free range around the yard all day.
About a week after getting them, we started getting one large egg a day. We observed many times that this large egg came from our barred rock. A few weeks after that, we started getting one small egg a day. We found that the small egg came from one of our three speckled sussex, who we can't tell apart unless they're standing side by side. This went on--one small egg, one large egg a day--for quite awhile. Then, after coexisting peacefully in the yard for all that time, our dog suddenly killed two of our chickens. He killed one of our NH Reds who had never laid, and one of the Speckled Sussex. The attack happened 12 days ago and we stopped getting eggs. I think it's possible that the sussex that was killed was our small egg layer, but how come our barred rock stopped laying? Then 5 days ago, we got three new chickens from the local classifieds. These ladies are supposed to have been hatched spring of 2012, and the lady said they were regularly getting an egg a day from each of them. Well, they haven't laid an egg since they got here! What is going on?! I have 7 chickens, not one of them is laying an egg, 4 are supposed to be 7-8mos old, and 3 are supposed to be a year and a half? I thought maybe they weren't getting enough light because their coop/yard is slightly shaded by a pine tree, so for the last 4 days, I've been allowing them to free range out in the sunshine all day, (with the dog carefully kept in of course). Still no eggs. (Also, I have literally crawled over every. single. inch. of our back yard several times a day. I GUARANTEE that there are NO nests back there.)
Whats going on here? I spent a couple hours going through all the "why aren't my chickens laying" threads, but just didn't see anything that seemed like it could be it. Also, I wanted to get your guys's thoughts on the recent trauma they've all experienced and how some were laying and now they're not, etc. Thanks in advance to you guys for any help or insight you might have for me!

 

Thank you so much for your replies. I knew that trauma could keep them from laying, but I just didn't realize for how long. I'll just keep going on then,, and hopefully they'll start laying soon. What about the other 2 speckled sussex and the NH red that have never laid? Do you think it's odd that they're going on 8mos and have never laid an egg?