Photographers would have come across this issue at one point in their shooting experience. When taking pictures of a bride and groom, sometimes one of them is not as sharp as the other. Unless your intention is to create a shot where for example the bride is sharp and the groom is considerably out-of-focus, you will very likely want both of them to be sharp. A slightly out-of-focus groom will appear like an error.

Use a Smaller Aperture
To the horror of those who love pictures with shallow depth-of-field, it is actually fine to use F4 or F5.6 when you are taking pictures of two people. Especially when you are using a long lens such the Nikon 70-200mm F2.8, which tempts you to use F2.8 because the background looks so good with F2.8. But beware, using a large aperture like F2.8 may render one of the subjects you’re photographing out-of-focus. Using F4 on a telephoto lens is safer when photographing two or more people. Make sure that you focus on the person who is closer to you, as the depth-of-field behind the focus point is more than that in-front. At F4 you will still be able to get a nice out-of-focus background because a telephoto lens inherently has shallow depth-of-field. Top it off with a relatively close camera-to-subject distance and you’ve got the recipe for a couple portrait with the blurry background you wanted. So don’t throw away that F4 telephoto lens just yet!

Mind Your Distance-to-Subjects
If you can subconsciously and consistently keep BOTH your subjects roughly the same distance from you when posing them, you can get them equally sharp, even at F2.8. This technique is great if your composition allows it. And there are many great posing combinations that can use this technique.

Watch Your Shutter Speed
Using the 1-over-Focal Length rule, your shutter speed should be dictated by your focal length. If you’re using a 200mm lens, your shutter speed should be in the region of 1/200 unless your lens has VR (vibration reduction) or IS (image stabilization). This will prevent camera shake, which results in blurry pictures. If your subjects (or you) are moving, you will need to increase your shutter speed even more.