More protein won't hurt but the fat content will help them gain weight fast. The corn will cause a deep yellow fat layer to be deposited. A high protein diet would have been beneficial when they were younger but not so much at this point.
ACV will not do anything good for your turkeys. It can actually be harmful since it interferes with the proper absorption of calcium. Vitamin B complex is with its niacin and thiamine will help with the leg issues.
If your sole purpose is to quickly reach maximum weight before processing, switch to high fat feeds such as BOSS and cracked corn. In order to supplement their diet with essential vitamins, use vitamin B complex at the rate of 1/2 tablet dissolved in one gallon of water. Make it their only...