  We present sub-arcsecond resolution ALMA imaging of the CO(3-2) emission in
two $z\sim2.5$ heavily reddened quasars (HRQs) - ULASJ1234+0907 and
ULASJ2315+0143 - and their companion galaxies. Dynamical modeling of the
resolved velocity fields enables us to constrain the molecular gas morphologies
and host galaxy masses. Combining the new data with extensive multi-wavelength
observations, we are able to study the relative kinematics of different
molecular emission lines, the molecular gas fractions and the locations of the
quasars on the M$_{\rm{BH}}$-M$_{\rm{gal}}$ relation. Despite having similar
black-hole properties, the two HRQs display markedly different host galaxy
properties and local environments. J1234 has a very massive host, M$_{\rm{dyn}}
\sim 5 \times 10^{11}$M$_\odot$ and two companion galaxies that are similarly
massive located within 200 kpc of the quasar. The molecular gas fraction is low
($\sim$6%). The significant ongoing star formation in the host galaxy is
entirely obscured at rest-frame UV and optical wavelengths. J2315 is resolved
into a close-separation major-merger ($\Delta$r=15 kpc; $\Delta$v=170 km/s)
with a $\sim$1:2 mass ratio. The total dynamical mass is estimated to be
$\lesssim$10$^{11}$M$_\odot$ and the molecular gas fraction is high ($>$45%). A
new HSC image of the galaxy shows unobscured UV-luminous star-forming regions
co-incident with the extended reservoir of cold molecular gas in the merger. We
use the outputs from the Illustris simulations to track the growth of such
massive black holes from $z\sim6$ to the present day. While J1234 is consistent
with the simulated $z\sim2$ relation, J2315 has a black hole that is
over-massive relative to its host galaxy.
