Why is my iPhone 4 and iPod touch 5 linked together?

I just an iPhone 4 and whenever I text it shows up in my iMessage on my iPod touch 5 why is this? They are linked together how do I undo this so they aren't linked together?

You loged in icloud or message.
Go to settings and I'll see.

I have my mother in laws old I phone 4s as she got an I phone 5 and they seem to be linked? Every picture I take comes up on hers etc, even tho we're on different networks and have different apple ids. Any ideas?