I often am asked how I shoot wide open with families - well it's all about the planes. You see, the distance forward and back in your field of view is made up of various planes. Where your focal point is and what aperture (f/#) you are at will determine how much and where your focus will lie.
In the example below you can see the set up, six little squinkies diagonally lined up about .5" apart. Shooting wide open (low F/#) will yield a very shallow depth of field. While the larger f/#s will increase that, allowing for more of your image to be in focus. So the trick to shooting wide open is to keep your subjects on the same plane. Keep them close together, and at varying heights to keep them on the same focal plane. Focus on the center-most point of the group and you are good to go!