Imo, and I’m no expert, you should certainly give them extra vitamins. I’ve had great success treating balance and walking issues with vitamin e. they aren’t growing well. At that age, they should be smoothly feathered everywhere but the head, and the small one should be larger. They should both be fat around the body so the heads look disproportionately small until their adult feathers come in. Even when Ive had birds who feather slowly, they’re still chubby around the middle by that age. The small one is concerning because his gait is very abnormal, it’s more like he’s skating, pushing to the sides. I know some people mix chicken feed with scrambled eggs, Meal worms, or cat food.
what is your location? Can you get Amazon or Chewy deliveries? If you can, I can recommend some feeds you can order.