On site family portraits are a fun challenge. Sometimes I scout a location out prior to the session (recommended), but many times that is not possible. To help you plan better for a location portrait, there are three general areas I start examining as soon as I arrive: light, backgrounds, and posing areas. Backgrounds and posing areas are perhaps the most critical. I want the backgrounds to tell something about who I am photographing and be structured in such a way as to not have distracting elements. I want the posing area to allow me to create an interesting flow in the picture so as to avoid the 'soldiers lined up in a straight line look'. In someways lighting is the least important, because with good strobes, I can modify the existing light fairly easily.
Here are a couple of pictures from a recent session on location. During the session, I am always looking for a few spontaneous shots as well to enrich the collection of pictures the client receives, such as the last picture in this series.