I have a doubt: if I buy the three DLCs, will I have to play them separately or are they added to the normal game or how? I just want to buy them
I bought the game on steam, they automatically get added to the game. Not 100% sure on here, but I'm sure they get auto added.
In itch.io you have to copy and paste them manually inside the game folder of the game.
game
The DLCs are added to the normal game, and happen at different times in the story, if that is what you mean. Sorry if I'm misunderstanding your question!