A hyper and a nervous rat (females)

Question
Hi :)
I recently bought a pair of female rats at my local pet store, I've had them for 3 days and now I have a few questions:

The smallest is very shy and nervous, unlike the other who is very, very hyper..
She pees and poops whenever she is held, i know its because she is scared, so how can I make her feel safe around me?

They also had a fight today, I don't know how serious it was, but it still made me wonder why the fought.. They could have been playing, but the smaller rat won't come near the other now.. She's just sitting in the corner?

Also, my bigger rat is overly hyper.
When she is sitting on my shoulder she will make some sort of teeth grinding sound, but she also bites or nibbles my fingers whenever i touch the cage or hold her.. Does she need something to chew on? Or does she not like being held?

Lastly, their cage is a bit small, but it is only temporary.
They're still quite small, a little bigger than an adult mice. The cage is about 12 cm deep, 30 x40 wide and 60 cm tall. When do you think i should buy a bigger cage? I mean, how fast do they grow?

Thank you for you time :)
Victoria

Answer
Please read my site, sandyscrittercity.com and read all you need to know about rats including the stuff you asked me in your message.  The grinding of the teeth is called bruxing and this means she is content and happy.  Her eyes may even vibrate while she does this.  Female rats are full of energy more than males, but all young rats are very hyper and fast.  Start with my website going to the HOME page first and read up on them, you will find plenty of info that you need about them from housing and diet to how to make new shy and nervous rats feel safe.  It will take a while for the shy one to feel secure and my website will tell you how to help her through this stage. Let me know what you think after you read it.