How to randomize 3 different objects in a row?

Hello.
I want to randomize 3 different objects in a row based on a specific position (e.g. x360. y700).
The random objects are not generated one per second.
During a special action event (pressing a button corresponding to each object color), the lowest object disappears and the next object in the sequence moves down to the x360. y700 position, and the objects behind it move down with it. Also, since one object disappeared, one new random object is created on top.

  1. how to generate random objects based on a specific location at the start of the game?
  2. how do I make all objects move down one level if they are correct by pressing the correct button for each color? Additionally, how do I generate the last object on top?

I have absolutely no idea how to get started.
If you have any relevant gdevelop examples, please let me know.