Quick question on movement

[Meglobob]

A large army is in a castle province with move orders to a neighbouring enemy province.

Forces teleport in to engage the army.

What happens?

1) Will the entire army fight the teleporting army in the magic battles phase of the turn?
Or
2) Will the army stay behind the castles walls. Leaving a battle between the teleporters vs PD and patrollers.
OR
3) As no. 2 but the army trys to carry out as much of the move order as possible and attacks the teleporters in the normal movement battles phase, assuming the teleporters defeated the PD/patrollers.

Help, brain hurts, can not compute, danger of overload...