  We report ultra-deep, medium-resolution spectroscopic observations for 4
quiescent galaxies with log$_{10}(M_*/\mathrm{M_\odot})>11$ at $3 < z < 5$.
These data were obtained with JWST NIRSpec as part of the Early eXtragalactic
Continuum and Emission Line Science (EXCELS) survey, which we introduce in this
work. The first pair of galaxies are newly selected from PRIMER UDS imaging,
both at $z=4.62$ and separated by $860$ pkpc on the sky, within a larger
structure for which we confirm several other members. These galaxies formed at
$z\simeq8-10$, and, despite their similar stellar masses, ages, and their
proximity, they exhibit very different stellar metallicities, hinting at
different formation pathways. These systems could plausibly merge by the
present day to produce a local massive elliptical galaxy. The other 2
ultra-massive quiescent galaxies are previously known at $z=3.99$ and $3.19$,
with the latter (ZF-UDS-7329) having been the subject of debate as potentially
too old and too massive to be accommodated by the $\Lambda$-CDM halo-mass
function. Both exhibit high stellar metallicities, and for ZF-UDS-7329 we are
able to measure the $\alpha-$enhancement, obtaining [Mg/Fe] =
$0.42^{+0.19}_{-0.17}$. We finally evaluate whether these 4 galaxies are
consistent with the $\Lambda$-CDM halo-mass function using an extreme value
statistics approach. We find that the $z=4.62$ objects and the $z=3.19$ object
are unlikely within our area under the assumption of standard stellar fractions
($f_*\simeq0.1-0.2$). However, these objects roughly align with the most
massive galaxies expected under the assumption of 100 per cent conversion of
baryons to stars ($f_*$=1). Our results suggest extreme galaxy formation
physics during the first billion years, but no conflict with $\Lambda$-CDM
cosmology.
