Multiple Questions

Question
Hi! I have four rats and have two questions. One is that one of my older rats, not sure how old she is, seems to be gaining a little weight recently. I have four female rats for sure. I try and let them out everyday and when they are out it is more than an hour at a time. I also feed them a very healthy diet. Any suggestions?
My second question is in regards to pairs of my four. Lilly and Nite get in occasional "fights", standing on their hind legs and bating at each other. Jazzy and Bates do the same also. I would really love to incorporate them into my one large cage but am afraid to do so. I have put them together under supervision; what else do you suggest? Thank you!  

Answer
1) Its normal for rats to gain some weight as they age. Just make sure she gets enough exercise and stays healthy.
2) Its also normal for rats to get into little scuffles as long as no one is getting hurt. It could be a good idea for you to combine the two pairs. Keep letting them play together outside of their cages and introduce them slowly.