the WP thumbnail images have the following properties: max-width: 100%; and height: auto; this allows them to scale to fit their containers, this way they scale to fit instead of distorting the aspect ratio when the screen is rescaled.
Best way is to ensure that all your original images have identical dimensions or at least the same aspect ratio.
Are you able to edit the images? If so create a template that can accommodate the tallest and widest of the images. Place each one within the template. And save them with transparent or white space around them. This way they will all be the same size.
Yes keeping them all the same width and height will solve the issue. You can always leave white or transparent space ( if you’re using a PNG file ) to create deadspace around them so the logo itself stays proportional.