If you click on the card, you'll see that the game text was errata'ed to say: "Each time a companion or ally loses a skirmish involving a Southron, you may remove (4) to make the Free Peoples Player wound a Ring-bound companion."
Due to this re-wording, the fact that there are more than one Southrons in the skirmish is irrelevant; however, the fact that you have two copies of Howl in play means that you can use each one once (spending 8 twilight), just one (spending 4), or none of them (free).