Technical difficulties are one thing but getting my son to put his arm around his sister is another. My daughter idolizes her older brother (knows how to irritate him, too) but my son is in a phase where all-things-girl are bad. Anyway, after much cajoling, I snapped the photo below. I know Halloween is still a week or two away but on that night, good photos are tough to get, so happy early trick or treat.
Early evening, the light is wonderful for portraits. Working on skin tones and smoothing them is a trick. I usually do it by getting the right color, softening the skin (with kids thats easy) and then bring up the light on the skin so that you get a bit of glow. The softer look needs to be offset by sharp, sharp eyes.

Together
Nikon D90 with Sigma 24-70 at 34mm. 1/25s at f/2.8, ISO200. In Lightroom, I adjusted white balance, light levels, increased vibrance and decreased clarity. Using the brush tool, sharpened and brightened the eyes. Adjusted red levels (for the Harry Potter scar and their lips), set mode to Portrait and adjusted, added a dark vignette and I was complete.