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.

How does targeting work when you cast an area spell?

When casting an area spell, the mage can choose to target a being, or a point in space.  Unless specified in the spell description, the area of the spell is a sphere of [Force] meters in radius, centered on the target.

When the spell is direct, the caster needs to see her target (with her natural sight, including through transparent objects, on a reflective surface or with sight augmentations that were aquired by spending karma).  Once the spell hits, every beings that the mage can see and that are located in the area will have to resist the spell, friends or foe.  It is not possible for the mage to use his hands, to hold objects or to use electronical device to hide a friend from sight, although objects in the environment can be used to hide from the mage or to limit the mage's sight.  Two persons holding hands or fighting at close range will always be both targeted.

When the spell is indirect, the mage can cast her spell without actually seeing the target, but there must be a clear path between the target and her.  Once the spell hits its target, all beings in the area and with a clear path from the target are affected, whether they can be seen or not (as with a grenade). 


Refs.: The core rulebook is unclear on target choice and line of sight effect (spellcasting p.281 and indirect combat spells p.283)