How do two or three people or more people focus when taking a group photo with a large aperture? ...

Focusing has nothing to do with aperture. Generally speaking, cameras are autofocus. You just need to choose the focus mode. You can choose single point and single focus or automatic servo focus, and you can focus the subject automatically, regardless of the aperture. Aperture is used to control exposure and depth of field. If you want to blur the background, remember the following principles: the longer the focal length, the more blurred the background; The larger the aperture (don't reverse the aperture), the more virtual the background; The closer the camera is to the subject, the more virtual the background is; ：