The problem is with fb only. It maybe caching the site content. You can verify it by first trying to post the url in facebook, which if cached, will show you older images. Then in object debugger, click on “Fetch new scrape information” which should try to get the latest code and tell you that
“og:image was not defined, could not be downloaded or was not big enough. Please define a chosen image using the og:image metatag, and use an image that’s at least 200x200px and is accessible from Facebook. Image ‘http://www.delladio.it/wordpress/wp-content/uploads/2014/12/P4250860.jpg’ will be used instead.”
Now it will show the 3 images link and despite them having required width, it will tell you “When shared, this is what will be included” with a different image. But when you try to post this url again, you can see that now it will allow us to select 1 of the 3 images for which the og:image tag was found.