Should everybody in the same household be treated for scabies?

This is the advice from the Norwegian Institute of Public Health, called Folkehelseinstituttet: 

"People you have close contact with should be treated, even if they do not itch. "Close contacts" in this context means everyone in the household and others with whom you have shared a bed, towel and the like. Everyone in the household should take treatment at the same time. This also applies if you live in a collective."

So yes, so you should all get treatment at the same time.