Image files twice saved for iPhone and iPad

I bought the My Cloud Home and have installed it at home. There are three devices linked to it - my iPhone, iPad and Laptop. All use with the same Apple ID.
If I start the sync of my iPhone and iPad on My Cloud Home, it downloads all images from the Apple Cloud of my iPhone and of my iPad. As a result, all images appear double. I don’t like to have the same file twice on my Cloud.
What do I need to change in order that the same image file is stored on My Cloud once only?
Best regards

@Philipp9 Disasble Auto Backup on one of the iOS mobile devices so that only one will backup the files located in the device Camera Roll.