I would also be worried about same sex aggression.
Not sure of what sexes your two dogs are? If you get a female pup and already have a female, or have a male and get a male...with only two years age difference there may big problems in the future.
I think having two 2year old dogs is a challenge already...add a new pup to the mix and you must worry about how much time and attention they will all get.
Gina