The courtesy exchange happens after the Charleston. Each of you offers zero to three tiles; the smaller number is what actually moves.
It is not the first round and not the second. Jokers still stay on the rack.
If someone stops the second Charleston, the courtesy exchange usually still happens.
Not a third Charleston
Courtesy comes after both Charleston rounds. You and the player across offer zero to three tiles; the smaller offer moves. If someone stops the second Charleston, courtesy usually still happens.
Jokers still stay. It is not the first round and not the second. You exchange only with the player across.
Jokers do not move in the courtesy exchange.