Is 'pens' 'Stiften'? I thought it was Kuli or Kugelschreiber. 'Stift' is more like 'Marker', right?
No, a "Stift" can be any sort of pen. "Kugelschreiber"/"Kuli" means "biro" or "ballpoint pen". The German for "marker" is the same as the English.
OK, but why can't Kugelschreiber be acceptable?
We don't know what kind of pens they are.