You can keep them together for about 3 months but keep an eye on their behavior. If one is bullying or posturing, separate them. Also if one is not growing as fast, separate. They may not be getting their fair share of food. I am currently raising 5 baby nosy faly and this is what i am looking for.
Sorry I havent been very active. Its hunting and hawking time but I did pick up some Nosy Faly from @Matt Vanilla Gorilla. Thanks again Matt. They are growing fast and Im excited to see the colors come in. All are eating like champs and some more than others.