Solved
Ghost won't sleep in same bed than other Sim
So I got a Sim off the gallery and I added them to my household.
The ghost refuses to sleep in the double-bed with my other Sim.
I'm new to the game - I don't know if this is by design or not.
They keep waking each other up.
Sims won't sleep in the same bed with another sim until they have high enough relationship with each other. So work on building friendship (and romance if you want them to) until they are friends. Then they should be able to share a bed.
Hope this helps.
