You can managed images also from Admin – ADD / Edit Property – Property Details – Property Media.
Make sure you upload different images for each property. If you use existing images from Gallery they will be automatically detached from the previous post and inserted in the new post.
Add your images
Change featured image (the first image in property unit, and in property slider) from here:
IMAGE SIZE REQUIREMENTS
– Property slider images with sidebar should be min 810 px width
– Property slider images without sidebar should be minim 1110 px width
– Property featured image should be the same size, minim 500px to fit in the infobox
Image re-size rules are set in general_settings.php. More info on thumbs: http://help.wpresidence.net/article/thumbs-and-various-image-sizes/