You may want to rethink some of these species. You're missing OH- and SO2(aq), not to mention S2O5^2-, and there is absolutely no molecular H2SO3 present. The problem is that solutions of anions of weak acids can be very complex with lots of different species present, but in small amounts.
Sodium sulfite dissociates completely to form Na+ ions with a concentration of 2.66M, and bisulfite ion with a concentration of very nearly 1.70M. The concentration of hydroxide ion is also 1.70M. This is why a solution of sodium sulfite is basic.
