Help: 2 month old chick can't walk

[Hot Chick]

I think he's a golden sex link roo but he can't really walk ,when he was little i beleive he ran around but now he's getting older and all he does is sit his other 2 brothers . He only moves a little before sitting down , he acts like a beoiler chicken but his other 2 Bros are perfectly fine , what's wrong with him

 

[Hot Chick]

I was told he was a sex link but I really think he's a broiler

 

[Hot Chick]

 

[Hot Chick]

He looks like this but what I don't understand is how his other brothers are different