[Tuna-Fish]

One creature can target only one square in one action (more with quickness of some kind).

One weapon with several attacks can only hit one monster.

Single square can hold 6 "size units" where humans are size 2, cavalry size 3, dragons size 6 and vaetti/hoburgs size 1. So there can be up to 3 normal infrantry in one square, or one inf and one cav and one vaetti, etc.

So, assuming human-sized opposition:
1. it can hit up to 3 infrantry, assuming they all are in same square.

2. it can hit one unit.

3. it can hit 2 units. Ambidextrity only reduces the attack skill reduction if doublewielding long weapons.

4. 4 targets.
4a: 6 targets in up to 2 squares!!! (champ trident gives quickness, undocumented)

Nattie with 2 swords of swiftness and champ trident is however a bad idea, because against numerous opponents it tires very quickly, after which it's high def is not very useful. Try champ trident and wraith sword for 4 targets and regeneration and reinvigoration. However, still give him amulet of regen (or cast personal regen) because with it he racks up afflictions 10 times slower.