Featured image size issue

Hi, I am in the process of adding featured images to posts from an older site being updated with this theme. A problem I am encountering is that for many of the people featured in the posts, the only image I can use is from their profile on LinkedIn. Many are smaller than the recommended size, all are square, and in several instances (with more to come) the squares are as small as 208px. This makes them display as the full sized square with a white space off to the side, looking out of place with the other rectangles. Many are 300-400px. This is likely to be a problem with future interviews as well. I need a solution which will make all of the thumbnails on the blog page be uniform in size. What can I do? The site is in development but the page can be viewed here Also, fyi, I have disabled the search in the primary menu because it wasn't working. I haven't located the source of the search field to the right of the logo which does work. If she were to decide she preferred the one in the menu bar and wanted the one to the right of the logo removed this would be a problem. Thank you