When I inspect your images I see http://cld.wthms.co/Ds8i
To make those images the same dimensions on that page you have 2 options,
- make your images square before you load them
- change the image settings in your WooCommerce -> settings -> catalog -> Image settings to match these settings http://cld.wthms.co/ICPu
With option 2 you will need to instal and run Regenerate Thumbnails from the WordPress plugin repository (I would link it but I need a 10 reputation to do that) to resize and crop your images.