First, Breathe...
The haunch thing you talk about... they kinda stand like that as adults so I wouldn't be too worried.
I'm not sure if that's a yawn but I see mine do that too. My daughter calls it yawning so...
Bedding = nothing slippery. I used to put pee pads with a rubber netting. I hear you can buy something like it at almost any store. Shelf liner. - not the slippery sticky paper

paper towels or a textured cloth could work for now but NOT newspaper.
As far as mereks I don't think so. I do know if you buy them from a hatchery (I just looked lol) they don't offer any vaccinations with them.
I'm not sure why the antibiotics...if they aren't sick...of course that's just my opinion.
Mine are healthy happy little fatties. I hatched them. Then fed them unmedicated chick mash and ground up gamebird crumbles. With dried mealworms ground in to make sure they got enough protein.
Now they eat gamebird crumbles and dried mealworms are the treats
Keep then warm, dry with plenty of food and water. These are hearty little birds. You should be just fine.
Feel free to yell with any questions at all. Of all my birds - Turkeys, ducks, guinea fowl, chickens (including bantams), quail and recently geese, I think the chukars are my favorite. They are so comical. Better than having a fish tank. I can sit and watch them forever!