are part 1 and 2 standalones or do i have to merge them together?
In fact, these questions can also be found by reading the description of the game or by starting to play.
It is logical that since the first part has chapters 1-6, it is first enough to install the first part. At the end of chapter 6, you are asked to install the second part to continue.
Naturally 2 parts are installed separately from each other. Otherwise, no one would divide these parts. (this is not a separation when archiving is carried out. but a separation of the game by the author, as the content has become too large to fit in one part)