Business Class is usually the first car after the engine (or bag car if there is one). Hopefully, being only the 2nd stop (assuming your train stops at BWI) after WAS, you'll be able to find 3 seats close to each other.
Betty the only thing that is slightly wrong with your post is that BAL is normally the 3rd stop after DC. New Carrolton is served by almost every NE Regional. But it's ok. You're close!
I would say it depends on when you're traveling. Time of Day and Year. This time of year is usually busy. People going to NYC for the rockettes and other NYC Christmas events. I can tell you that Business Class has 2 Four Seaters that have a table. Both are at one end of the car. It can be a bit of a bouncy ride. The tables are over the wheels of the car.