Trying to get a customized gallery layout in 7.1

Hey all - looked high and low all over Google and couldn't find anything quite like what I'm hoping for. I'm trying to design a portfolio site with a custom image gallery.

Ideally, I'd like something like this (2 normal sized thumbnails next to each other, banner style long one below them) - https://www.elisha-edits.com/

But here's what I currently have - https://www.richardjamescook.com/film-and-video-work-new-classic

You can see I've *kind of* achieved it with CSS, but my sections are separate, which isn't ideal for mobile resizing (leaves huge gaps between). I also want my image blocks to crop responsively like the first site I posted.

I'm unable to find anything to code this into the same section. Can anyone help?

*note: I know fluid engine can achieve this layout, but I'm not ready to switch to it since it's still in its infancy, is missing other features I use, and quite buggy atm*

Edit: Kinda got what I wanted by stacking image blocks in a certain order of duplicate/drag - but now dealing with a padding issue between the top image block and the one below it. Have CSS overriding padding (check my homepage), but it appears to make no difference when it's not a single image block on top of another one.