I recently picked up a 2-umbrella flash kit from my favourite photography shop which included stands, umbrellas and flash mounts. I also recently picked up an off-camera flash cord to use with my master flash unit.
I found that this setup worked well if I was not moving around too much and stayed within 4 or 5 feet of my main flash unit. I might either pick up another off-camera flash cord, or get either another slave flash unit or the ST-E2 wireless transmitter.
I had used the pair of flash units in the past and found that the umbrella setup works much better at getting the light where I need it. Making sure that the subjects were about 3 feet from the back wall also helped at eliminating shadows. My main flash unit, at camera left, was set at eye level pretty much horizontal and the slave unit, at camera right, was set higher and angled downward at about 20-30 degrees. Each umbrella was aimed at a 45-degree angle to the subject to illuminate the eyes and face to get rid of shadows cast by the nose and cheekbones.
The window at the back left corner also provided some natural light so I had many of the shots where the subjects faced their shoulders directly toward the main flash at camera left. The window provided light for the hair and shoulders. I then had them turn their head back facing between the umbrella and the camera with their eyes looking at the camera.
I had the slave unit at camera right set to +2/3 and the master unit at camera left set to +1/3 to provide some fill flash.