Specifically 13th century pre-cannon era medieval armies. Like you might see a few cannons around but they're largely not normal and considered very new/dangerous. The primary kingdom does not possess any.
A rival kingdom with inferior numbers possesses magical archers that can fire arrows over 2 kilometers away. With the exception of range- the arrows function as normal arrows.
For example, if the max range for a normal archer was 200 meters and could go into a human body, these magical archers can have the same result at 2 kilometers. If the normal archer can hit a bullseye at 100 meters, the magical ones can do so at 1 kilometer due to the magical nature of the bows allowing them to see 2 kilometers away just as easily as a normal archer could see 200 meters away.
The arrows will always survive the flight- no breaking from being fired so hard etc. They also correspondingly would be stronger the closer you made it towards the archer- though when they strike something after being fired they're no more durable than a normal arrow. Said archers create arrows without effort every time they draw back their bowstring- though firing the bow takes as much effort, again, as their normal counterpart when related to range.
If an army of say 5,000 with appropriate amounts of every troop type were to attempt to cross through a pass guarded by 4 of these magical archers, 2 on either side, what strategies could they use to hopefully pass with the least damage to their numbers/VIP soldiers?