Custom Gallery images showing in one column
Its has multiple ways to do that but I recommend you to do it with views.

Create a new views as block view and follow the following steps:


Add image field in fields
Add filter criteria
You can change the FORMAT of the views as you like (according to your requirement you should select Grid type) to display images in multiple columns.
Add a contextual filter with nid (node ID) field and set it like this 
Save the views and go to admin/structure/block and enable your block
Don't forget to hide the image field in the manage display of Gallery Content Type, path is admin/structure/types/manage/CONTENT-TYPE/display


Image as Example


For more details, click here