One month ago we got the little guy. Now look the little one is the same size as the other one. They eat the same get soaked the same. Why is one growing faster?
Could be he is catching up from poor care from before you. Could be the other, larger one is being bullied, could be genetics, lots of things could be the reason. I would just keep doing what your doing and make sure there is no bullying and they should grow nicely.