just one at a time. Can you open them all at once and if so, how? The Help functions associated with this software are not that helpful and I could not find out how to do that from Adobe documentation.
Go to the folder that the photos are in, highlight the ones you want to open, right click, and choose to open with Photoshop Elements 14. You should have them all opened in their own tabs. Just click on the tab of the photo you want to view.