Using bathroom everywhere/getting older

I recently got 3 chinchillas, two 2 month old's and one 4 year old. I noticed that one of my 2 month old's is peeing around the pee tray and not in it. My other 2 month old is not doing this, also neither is my 2 and 4 year old. Is this a normal thing or?? Also I was wondering since I have 2 month old's what should I look out for when they start getting to that puberty age. Are they going to start not getting along with the 2 older one's, even before I got them they were housed with the chinchilla I have currently( was acting as their mom before I got her) and when I got them I also got the older chinchilla who was acting as a mother for them currently. They are all getting along great especially the 2 older one's, I was kind of worried they wouldn't after hearing people's stories of how it's harder to bond 2 older chins then it is 2 younger chins. Any advice/answers would be greatly appreciated.

(All my chins are female)