Do spells hit entities in both physical and astral plane simultaneously when you are dual-natured?

Yes.  When you are dual natured, you cast in both planes simultaneously.  This means that area spells will target both the entities in the physical and the astral plane.


Note that since your sight will be in astral, some objects from the physical world such as windows may become opaque to you, limiting your line of sight and thus protecting potential targets on the physical plane.  Also, it has to be reminded that only mana spells work on the astral plane.