In WordPress, by default a “gallery” contains all images attached to a post. It is possible to insert more than one gallery in a post by using the ‘include’ option within the gallery shortcode. Upload your images to the post as usual, and in the “gallery” tab of the media-manager, try and identify the image number of the attachment. In chrome, you can right click on the image and click “inspect”.
Then, insert the gallery using the gallery shortcode, using the include option (make sure to wrap in square brackets):
gallery include="460,459,458,457" link="file"
The gallery above includes images 460,459,458,457, the gallery below includes images 456,455,454,453.