Depending on how close you are to the A train and which terminal you're going to, it should take you around an hour or a little more and cost $7.50 per person. I'd leave around 6pm, which is rush hour, so it will be a bit busy but you'll probably get a seat at some point in Brooklyn as people get out.

By road from lower manhattan there's no great route. Atlantic Ave might be a good option that will avoid rush hour traffic on the highways, which can be very bad. I'd expect at least an hour drive at that time, possibly 1.5-2. And you'll need a mini-van for 5 passengers.

Don't forget to read this:
http://www.flyerguide.com/wiki/index...sportation_FAQ