Actually, what I want to do is to make 3 npcs sleep on a special bed, and use custom animations.
If you load for example NobleBedDouble01, there are two Markers in "Active Markers" list (you can see the blue npcs in the preview window), but I cannot add new ones. Where are these markers in the CK? Are they stored in the CK, in the model file or somewhere else? They are called "Sleep 0" and "Sleep 1" and you can enable/disable them. I opened the nif mesh in nifskope, but I didn't find those two markers.
Let's say I want to add a "Sleep 2" marker to this bed, where do I specify the proper animation to play when npc enters bed or sleeps?