  Massive, starbursting galaxies in the early Universe represent some of the
most extreme objects in the study of galaxy evolution. One such source is HFLS3
(z~6.34), which was originally identified as an extreme starburst galaxy with
mild gravitational magnification ($\mu$~2.2). Here, we present new observations
of HFLS3 with the JWST/NIRSpec IFU in both low (PRISM/CLEAR; R~100) and high
spectral resolution (G395H/290LP; R~2700), with high spatial resolution (~0.1")
and sensitivity. Thanks to the combination of the NIRSpec data and a new
lensing model with accurate spectroscopic redshifts, we find that the 3"x3"
field is crowded, with a lensed arc (C, $z=6.3425\pm0.0002$), two galaxies to
the south (S1 and S2, $z=6.3592\pm0.0001$), two galaxies to the west (W1,
$z=6.3550\pm0.0001$; W2, $z=6.3628\pm0.0001$), and two low-redshift interlopers
(G1, $z=3.4806\pm0.0001$; G2, $z=2.00\pm0.01$). We present spectral fits and
morpho-kinematic maps for each bright emission line from the R2700 data for all
sources except G2. From a line ratio analysis, the galaxies in component C are
likely powered by star formation, while we cannot rule out or confirm the
presence of AGN in the other high-redshift sources. We perform gravitational
lens modelling, finding evidence for a two-source composition of the lensed
central object and a comparable magnification factor ($\mu$=2.1-2.4) to
previous work. The projected distances and velocity offsets of each galaxy
suggest that they will merge within the next ~1Gyr. Finally, we examine the
dust extinction-corrected SFR(Ha) of each z>6 source, finding that the total
star formation ($510\pm140$Msol/yr, magnification-corrected) is distributed
across the six z~6.34-6.36 objects over a region of diameter ~11kpc.
Altogether, this suggests that HFLS3 is not a single starburst galaxy, but
instead is a merging system of star-forming galaxies in the Epoch of
Reionisation.
