You don't necessarily need to take two shots. You can either use flash to illuminate the foreground subjects or a technique called light painting.
In either case you are illuminating the foreground for a very short duration of the much longer total exposure that includes the sky.
With a long enough exposure, you can light your subjects with a low power flash or paint them with any other light source in a short time span. Once the light source is turned off (or the flash has fired), the people can move out of the frame very quickly and their movement will not even show up in the exposure!
Note that there are two main approaches to light painting:
- using a switchable, movable light source from outside the camera's field of view to selectively illuminate specific portions of a dark scene.
- using light sources inside the field of view of the camera and moving them around during the exposure to create drawings with the light trails
Sometime these two approaches are combined in the same image. For the photo you wish to make, you only need to use the first technique.
Although this article is aimed at producing star trails, the advice for lighting foreground objects is spot on and applies just as well to single long exposures.