As an aside, bare flash can be made to work pretty well. Put the camera in manual, meter for the sky, underexpose the sky by about 1 or 1.5 stops, then use the flash to make up the difference on the subjects. You may need to turn down the power on the flash a good bit to avoid blowing out the faces.
In the shot below, I used a bare shoe mounted flash. The sunset had already dropped below the horizon. Not the best, and there are some reflections of the subjects' skin - but if it's all that's available, why not try to make the best of it?
