They look normal to me. At that age they always look like they have outgrown their feathers. Be prepared to up that feed amount as they grow. According to my chart, they should be eating .324 pounds per day per bird at 4 weeks. That will increase to .5 pounds per day per bird at 8 weeks.
Sounds like Pulmonary Hypertension causing ascites. That bulging rear end is ascites (also known as "water-belly" It's the result of the fast growth rate of CX and the inability of the heart/lungs to keep up with the oxygen demands. If they got chilled in the early days, that will accelerate...