Additional Arm

The Homunculus can perform an additional attack ACTION in Melee or Ranged combat without any penalty. Therefore, if making attacks with three melee weapons, only a single weapon would need to be declared an Off-Hand weapon (suffering the appropriate penalties). It has three hands to carry weapons if combined with Human Hands, and may equip weapons and a shield in any combination, as long as it has hands free to do so. 

In this case the Homunculi can make up to two Ranged Attack ACTIONS (if it has sufficient weapons and number of hands to carry them), and up to three Melee Attack ACTIONS (if armed with three one-handed weapons); or one Melee Attack ACTION with a two-handed weapon and one Melee Attack ACTION with a one-handed weapon.