York Main Gallery Page: make all feature images square (not full width)

Hi there, I'm working on building project pages for my gallery, and on the main "Work" page that shows the featured images for each project, I'd like them all to be square. Currently they alternate rows: square side-by-side, then full width image, then side-by-side squares, etc. 

Here is a screenshot (site is not live yet). The lower, greenish section I'd like to become smaller and a square so that another image can be side-by-side. 

Thanks!

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