Featured Image Size

I have pages where I embed my WordPress posts. This usually displays the featured image and a preview of the text. Up until recently, all of my featured images in the embedded posts would be the same size. Now they are usually rectangular which weirdly crops my photos and isnt consistent with other embedded posts on my page. How can I get all of these images to be the same size and shape?

You can see an example on my homepage here. The first 2 are rectangular and the last 2 images are square. Any help is appreciated!