To begin to take this dream apart, one has to realize that each character in the dream represents a part of the dreamers psyche or mind. Men tend to go with action part while women usually represent emotional parts of the mind.
The first step is to find out what his brother and his girlfriend separately represent to the dreamer. His brother was younger and impulsive and extroverted and social. So his brother represents action. The dreamer himself was a passive accountant who was introverted.
So the dream is calling for the dreamer to be more extroverted and somewhat impulsive. His subconscious is trying to move him from being passive into being more actively involved with others. A new baby represents a new part of the dreamer’s mind. In that way, it represents new potential that is being developed.
This is what the dream means on the first level. The dream is also true on the second or interpersonal level. He recently started to date a woman who used to date his younger brother. She was very extroverted and social. The dream was calling for him to develop the qualities of being more social while giving approval to his recent dating. When both levels collapse together like that, we call it condensation.