You have said that you have 4 teams working for the LS content and they cycle one in 4 month.
How about adding the whole content all at once every 4th month and not adding it little by little every 2 weeks? I think This will make the content more solid, bigger and actually will be enjoyed by the players.
The festivals are not content like a LS so they can happen independently from what the LS is adding to the game
Also, you can add bug fixes and other polishes every 2 weeks so people will know you are always improving the game.
More content added all at once is better then spread around in 2 weeks schedule.
Players will have enough time to finish it in their own pace without missing different parts of it.