Welcome to the forums. You don't need to worry about that, your pictures are not duplicated in different places. Every picture is saved only once in your phone, in different folders depending on the origin of that file (photo you took, pictures you downloaded, files received through a message app ...).
Gallery or Photos are just apps that read the media files that the Media Scan found all around your phone. The pictures are not saved in these apps and you can have as many gallery apps as you want without duplicating the original files.