Just wanted to chime in with my own recent experience. You've gotten good advice and I would echo to not jump the gun and see how the lame ones do. I think if they are curling their toes it seems more like a vitamin deficiency (although that's obv. not 100%). Most of my reading, and my one young pullet who had Marek's, could not curl her toes. She seemed to not be able to feel her foot at all. She was non weight bearing on one leg and after a couple days learned to pick her bad foot up and out of the way to hop but she was a very large bird and she had too much weight to be throwing it around on one leg.
I will say, though, that she was still happy to eat and drink the day I put her down. She wasn't feeding herself much because it was hard for her to get around, but she ate voraciously if I hand-fed her. I sent her to the state lab and they ruled caused of death as Marek's and she also tested positive for MS, though the pathologist's findings (lesions, growths, and suspected nerve impingement) were more consistent with Marek's.
I gave my bird 10 days to see what she was doing and if she might turn around. I had just had one be put down from tumors that I suspected were Marek's, so I kind of knew what was wrong. I'd say if your birds aren't turning around with vitamins and other supportive care, and they don't seem to have sprains or fractures, you might more seriously consider putting them down and having them tested.
