Different structure for each post

So I’m writing my own theme and my client has a specific structure they want.

The first image should take the full width of the container.

The second and third images should nest next to each other and take up 50% of the container.

The fourth image should again take the full width of the container.

This format should be repeatable and continuous but I’m not sure how to do it. Here’s my structure so far:

https://pastebin.com/B4hYpw1P

Here’s the link to the site. As you can see, the post is repeated for the four images before the next post takes up the next four.

Cheers.