Unfortunately, at this time, it's not possible to add multiple images in a 2 or 3 column layout style the same way you can on your landing page.
We do have a recommendation for creating a columned layout, though! It may require a little extra work, but we advise creating an image in a 3rd party editor (Photoshop, Preview, etc.) that would include all the images in the desired layout, and then adding the single image via an image element into the email.
2 images you see below that you want to have side by side cannot be in a column layout style in the Email Sender.
However, after you use a photo editor like Photoshop or Preview, you can edit the image you want it to look like and upload that image to your Image element.
Say you wanted a column format from your landing page in your email--you can take a screenshot of those columns and upload that screenshot to your email.
Since there are limited Display and Positioning options within the Email Sender to ensure your email displays properly across multiple email platforms, designing an image outside of Splash and then uploading it to your email is the best way to achieve a more advanced layout.