Astronomical models show that Alpha Centauri could retain planets in stable orbits out to about the equivalant distance of Mars.

Regarding the unlikelyhood of life developing so close to our solar system, another consideration is the fact that Alpha Centauri is around one billion years older than our sun. A lot can happen in a billion year headstart. On the down side, they've had a billion years longer to be exposed to catastrophies.

With orbital instability in the outer reaches of the AC system, odds are pretty good there have been more extinction level events to deal with. Life there could be developing all over again at this minute.