I wonder if all these ‘moons’ are actually debris from a relatively recent collision. I know that Pluto and Charon are mutually tidally locked, but I don’t know about Nix, Hydra and the new one.
The leading theory from Boulder is that the moons were formed after Pluto & Charon formed. I don’t think we know enough about the new moons to know their rotation periods. They are in different orbits from Charon, so the most they could do is always show the same face to Pluto.
Pluto’s got relatively no competition, so stuff that wanders by (which will be moving fairly slowly in relation to Pluto) is much more likely to be captured, and as a capture would have cockeyed orbits until they either get chucked back out, or run into Pluto or one of its moons, or over a period of time interacting with Pluto and its other moons, wind up in a more regularized orbit.
That said, Neptune’s moon system is haywire, with one of the three largest ones nearly at escape. Neptune’s more massive than Uranus, which has a rotational axis nearly in the ecliptic, but a nice normal moon system. One way to interpret this has been an encounter (sometime in the past) with a passing star. That would of course mean that the Uranian moon system was acquired later, after the encounter which tipped Uranus, but managed to get regularized quickly; Neptune managed to *not* get tipped (although without knowing what its axis was like before this hypothetical encounter, we can’t say that for sure) but nearly had its moons torn away.
Harrington and VanFlandern postulated an encounter with a planetary body possibly still in orbit around our Sun, which caused these phenomena. In addition, Pluto is an escaped moon of Neptune under this scenario.