Hi, Rob, and welcome to WikiTree.
Rob, I usually put a photo with more than one person in the profile closest to my direct line. After I’ve loaded the photo, the new page shows the details, etc, and further down in the left is a place to add others as subjects in the photo. Clicking the buttons beside the names in the list and adding them will add this photo to those profiles, too. I hope I got this right. Try it and see,