I can merge threads but not posts, especially across threads. So, you would need to use a copy-paste of your posts to the main wiki page. I recommend to click Edit in the source post and copy the content then paste it to the destination post.
So, do you still want that I merge threads? Your Part 2 and Part 3 posts will appear as comments in the thread Part 1, original threads will be deleted, if there will be no other posts.
I might be able to merge the messages in the thread later, not sure about that, usually it works automatically as a hint for several consecutive messages from the same person.
However, you might also consider to make them like this: