Where are you importing the photos from? What format files are you importing. If you are importing from an application (like WhatsApp) on a phone, even though they may be jpg files, they may not have a standard format and need to be saved by a more simple program before importing them. I shall await your response before giving more details.
As I suggested, if your photos are coming from a phone application they may not be in a standard format for jpg files. There are various solutions to make them compatible with Elements. You haven't told us what kind of phone you have or whether you took the photos directly on the phone, or whether your family sent them to you on an app. So, another possibility is that you have transferred HEIC format photos that you took on a newer iPhone. These files are not compatible with Elements 15.
If the photos came from your family via a phone app such as Whatsapp, here are some solutions:
Open the photo files in the Windows Paint or Photos apps and simply Save them.
Open the files in the Elements Editor, using File>Open in Camera Raw, then Click the Open Image button and then use File>Save As a jpg
I have recently found another option which you may want to try because it allows you to select many of these "bad" images and fix them with a single context menu command. It is a free utility called SageThumbs which you can download here. Here is a screenshot of the right-click context menu. Even though the problem images are probably already jpg, you use the Convert to JPG option to save them and Elements will recognize them:
If you are not comfortable working with such utilities, then try one of the first two suggestions.