I am stuck at a part where the sister is regularly pregnant, I haven't met the mother's sister even once & everything says wait
Look at the splash screen on the main menu:
Everything I circled is in the version you are playing.
Diane's content - what you are looking for is indicated by the red arrow.
The preview of the tech-update build that you are playing does not have all the old content migrated into it from the stable build (v0.20.16) of the game.
To learn more, read the changelog that is indicated by the green arrow.