After getting Weasel's quest regarding him, I followed Garth from a distance, and confronted him as soon as he started talking to Cutter, who interrupted me and then they both attacked me. After tanning their hides they were both pretty chatty, though. Garth returns to the alchemist's shop after the fight, if i remember correctly.
Did either of them give you the weed package? I forget which one has it but both of them have dialog after the fight, you get the package and that settles it for the two of them.