Walking troubles

[Shanusa]

I have five 10 day old Marans chicks that I picked up in person from a very reputable, local breeder that I've gotten healthy birds from before. However, 2 of the 5 (and of course it's the two I'm thinking might be hens) were fine for the first 5 days that I had them, but the one (and then another one day later) started having trouble walking. Stumbling, falling to one side with wings out, etc. Their legs look fine and if they manage to stand, they appear okay. They are on medicated food (I have always started chicks this way and have never had problems) with an electrolyte/vitamin mix in their water. Yesterday I did get nutridrench of their water instead. They eat and drink fine. When it was just one chick, I figured injury or a deformity, but now that it is two, that seems less likely. Any advice? I have bought 8 Marans chicks this year, 3 have been roos (two more are looking to be), so I would REALLY like to save these two most-likely hens if I can (although I want to save them if they were roos too).