ReikiStar has it right. I would also keep adding that ACV in the water. It really seems to level out my girls.
I'd put them in the tractor, too. If it gets below 70 at night, maybe bring them back in at night. Is there a secure coop in the tractor? I put mine out at 4 weeks (5 chicks were driving me buggy in the garage), and they have adapted quite nicely. Last night all 5 of them were stuffed into one nest box and I had to physically move two of them to a different spot. I'm not fighting them over the nest boxes because they won't be living in the tractor/hoop after they reach full size. I'll integrate them into the other group (11 months old) when they are around 16 weeks.