Los trabajos que empiezo en Photoshop pesan exageradamente mucho

You are comparing two completely different files built in two different manners.

If your friend built the same size document with the same number of layers and used the same embedded smart objects, you would both have the same file size.

But because my classmate's file weighs less, if we both follow the same directions and he has more images and layers

You have smart objects embedded in your many layers. That will add to the overall size of your document increasing it by the size of the placed graphic - think nested bowls, add one inside another and you get the weight of both.

You can rasterize those smart object layers if they are not needed.

The image (01 and 02) are from my partner and the other images are from my project, we did almost the same but my project weighs much more

What you might try is this: Get the exact dimensions in pixels of the problematic document. Create a new document that size, bit depth, and color space. Drag and drop the first bloated image (layers or, if you desired, a flattened version, so just the background) into the new document while holding down the shift key. Save the new document; is the size the same or smaller? 

There are many factors that can add to file size increases including overall pixel dimensions (w+h+resolution) and the number of layers. When saving a jpg, embedding color profiles or excess metadata can also increase that file format's overall size.

Can you share a screen shot of your file that is 9GB with the layers panel and give us the size from the Image Size panel?