On the Steam version all of the episodes should be free once you bought the original game as far as i am aware, so i presume that they are the same on itch.io and the be included with the game price, but hopefully the developer will let us all know.
If you follow them on twiter, it might be easier to ask for clarification on the prices (if all episodes are included with price of game or if every episode is charged seperatly).
I bought both CK1 and CK2 on steam long before i found out about itch.io, so wont be buying again in itch.io as i can not afford to.