This may be The Witches of Karres, a 1966 novel by James H. Schmitz. There was a 2004 sequel, The Wizard of Karres, written by Mercedes Lackey, Eric Flint, and Dave Freer long after Schmitz's death, and another sequel from 2010 by Flint and Freer.
The original novelette that forms the beginning of The Witches of Karres may be better known than the full volume. It was reprinted in numerous anthologies. So you might have read either version. The story features space pirates and space witches, and the 2004 sequel contains the word "vibro-knife," so the original may have as well.
The beginning of the plot, according to Wikipedia:
Captain Pausert is a well-intentioned but inexperienced merchant traveler from the planet Nikkeldepain, voyaging solo on the old pirate chaser Venture. While on the planet Porlumma, the captain is moved by sympathy to purchase three young sisters – Maleen (about 14 years old), Goth (9 or 10), and the Leewit (5 or 6) – who had been enslaved while visiting another planet on a jaunt of their own. In getting clear of Porlumma, the Venture escapes pursuit when the girls desperately use what they call the Sheewash Drive, which enables far faster transit than is possible with primary or secondary space drives available either in or outside the Empire. The girls reveal that they are witches from the planet Karres, with klatha (psionic) powers. The girls’ powers, but especially the possibility of this incredibly fast drive, draw the unwelcome attention of planets and ships they pass. After taking the three sisters to their homeworld of Karres, the captain attempts to return to his home planet but is stunned when faced with a barrage of criminal charges, many relating to his encounter with the witches and his brief stay on the prohibited planet of Karres; in addition, the planetary government avidly want the suspected new space drive. Captain Pausert escapes the Nikkeldepain police and military with the help of the middle sister, Goth, who had stowed away on the ship.