Also what is a good setting for getting the whole frame in focus, I have only been get certain parts of an image in focus when I want to get everything in focus?
Since you're using a 5D Mark III John, you may want to try setting the AF to 61-Point Automatic Selection AF rather than Single-point or AF Point Expansion settings. Of course, at 61-Point Automatic Selection, the camera will still focus on the nearest subject. So if you're taking a photo of several subjects, you will want to set your aperture higher such as f/4, f/5.6 or higher. Obviously the higher the aperture setting, the more depth of field will be achieved and the longer the shutter speed will be. Also, as some have stated, this will also largely depends on the distance of the camera to subject, as well as the relation of each subject to each other. I suggest if you're taking a photo of two or more persons is to have them stand closer together with their faces as close to one plane as possible. If it's a group shot with multiple planes of people, ie. people standing front and back, I'd recommend shooting with a tripod and timer/remote. Depending on whether you're shooting in Av (aperture value) or Tv (Time value) or M (Manual) you will want to make sure the shutter speed is high enough to account for handholding shakes. If shooting with a tripod, you can set the aperture much higher, to f/8/f/11+ but you will need to have your subject hold still for the corresponding shutter speed value which will likely be longer depending on lighting. Any movement during the exposure will be out of focus. The more light available, whether existing or artificial, ie. flash, strobes, etc., will allow for the higher aperture value and faster shutter speed.
Hope this helps.