In theme we have 3 design types for property unit.

The images that show in the card unit are a thumb version (smaller size version of the original images) which help with speed optimization.

The thumb is generated in wprentals/libs/general-settings.php 

The specific line that creates the thumb is

 add_image_size('wpestate_property_listings' , 400, 314, true);

Files with the code for the unit types are, 2 places). Images are resized using resize rule: wpestate_property_listings

You must edit the php files and replace resize rule twice from unit type you have setup in theme options with full.