I am pretty sure that is scale. Sometimes, people say you can kill the scale insects by using rubbing alcohol on a q-tip and rubbing on the spots. I tried it, but then my succulent looked awful. I got rid of mine. Maybe others have better ideas-but I would move it away from other healthier plants.

To make sure it is scale, try to wipe them off with a cotton ball/q-tip moistened with rubbing alcohol (or even a tissue). Scale would come off easily, with just little pressure. If squished, there would be red 'goo' - blood. Otherwise it is not scale.
In last photo, the tips are white (not brown). Could be just drying of the leave or it may be mealies. Is there any fluff? cottony-looking very fine webbing? See if it could be wiped off.
Are they all potted in communal pot? Some have different watering needs.
Btw, 6feet away from window is typically not enough light for most succulents.

Rina