And there were four leprous men. — Literally, And four men were lepers.
At the entering in of the gate. — And so outside of the city. (Comp. Leviticus 13:46; Numbers 5:2-3.) Rashi says they were Gehazi and his sons (!)
Why sit we? — Or, Why are we abiding? Nobody brought them food any longer, owing to the pressure of the famine.