You would create a conflicting situation. They will make with each other before sexual maturity, but will start killing each other later after 2 years of age. Males you can have as many, as you like, they will constantly go into fight, because it is typical of males to threaten each other position in hierarchy, but that is what just happens time to time. Females are different, even two sisters would hate to live in one territory where, their instinct tells them, they might raise puppies. If you want two females - the age difference should be not less than 3 years. Unless, of course, you neuter them at the earliest age before they started disputing.