Agressive rats...out of no where

Question
I've had pet rats before...all with different personalities and everything...so I thought I knew about rats, but guess not. I recently adopted 3 baby male rats, they were extremely sweet and loved being played with at 1st, then out of nowhere they all got very mean and antsy. I don't know why or what to do.
Just to give you some insight on my housing situation at the moment, we have quit a few animals, so I don't know if they're smelling my male chinchilla or a baby boy kitten. My cat(s) have gotten up to their cage and I'm not sure what happens...I suppose nothing because when they climb up things fall and scare the cat off, and also the other day I made some veggie taco meat...which smells like real sausage and they seemed to have gotten all excited over that. I haven't played with them for a few days due to a family emergency, but my other rats have gone some time without being played with and never got mean.
SO anywho, I don't know what made them mean and if theres anything I can do about it...I was wondering if you had any suggestions?

Answer
Would you say the boys were around 6 months of age or a bit older now?   What type of diet do they eat on a daily basis, and is there food available to them at all times? What type of exercise do they get when they are out of the cage?

I can help better once I know the answer to these questions.