Looks good to me, but it's easier if you don't know the subjects. Did you go through the Gimp/Inkscape process or is this a threshold rendering?
The first glance at a portrait hits the eyes. You can add a lot of reality to a portrait by adding the eyeball highlights, even if the photo doesn't clearly give them to you. They have to be consistent in all eyes to look right - at about the same location and usually not in the pupil.