Does anyone know a way to code this image grid to show the images at equal sizes?

I am creating a website for an animal shelter and am trying to make the page showing animals available for adoption look nicer.

It currently looks like this: https://broccoli-flatworm-p86s.squarespace.com/adopt

But I'd like it to be more in this style, with all the photos even in size:

Does anyone know what the coding would look like for this? So far I have as below, it may not all be relevant, I've just picked coding as and when to try and fix it! I'm very new at this...

Any advice would be appreciated!

Thanks,

Anna