You can use two of your 4' tables and have 2' to get around behind the tables. If the 4' table are only 2' wide, like mine are, maybe you could fit one of the 6' tables behind them, for extra depth, and then squeeze yourself into the side.
I think this calls for putting pencil to paper - draw a scale diagram of the space and your tables and chair and play around!
How much is the booth fee? I'm probably too cheap to get two spaces, so would squeeze my wares in, but that's just me!