I'm sorry if this sounds too religious, but I can only offer from what my Buddhist teachings give.

Rebirth is a result of our karma. When we die, our mind leaves our body and enters an intermediate state known as the Bardo. There, it "drifts around" for a while until karma "blooms" and it is pushed in the direction of its rebirth. That mind is neither male nor female, it only carries with it the imprints from it's previous lives. It then is born as a boy or girl or whatever its karma is.

It is very possible that you could have been your brother (it doesn't mean you are, but that you were). Interestingly how the timing works out. A child will carry with them the imprints of past lives so it's possible that you feel comfortable with your brother's name and personality (or maybe some other Andy ...) because you used them previously. (Not really you ... it gets really complicated fast.)

There was a case in England where a child's first words were dog whenever she would see a dog ... but she used the Tibetan word, not English even though her parents couldn't speak Tibetan. Possibly an imprint from her previous life.

Very long story short, from my own little perspective, its quite possible you could be the reincarnation (reborn is a better word) of your brother or are at least have a very strong karmic connection to him.