  We present a study of the physical and chemical properties of the Extended
Green Object (EGO) G19.01$-$0.03 using sub-arcsecond angular resolution Atacama
Large Millimeter/submillimeter Array (ALMA) 1.05mm and Karl G. Jansky Very
Large Array (VLA) 1.21cm data. G19.01$-$0.03 MM1, the millimetre source
associated with the central massive young stellar object (MYSO), appeared
isolated and potentially chemically young in previous Submillimeter Array
observations. In our $\sim0.4''$-resolution ALMA data, MM1 has four low-mass
millimetre companions within 0.12pc, all lacking maser or outflow emission,
indicating they may be prestellar cores. With a rich ALMA spectrum full of
complex organic molecules, MM1 does not appear chemically young, but has
molecular abundances typical of high-mass hot cores in the literature. At the
1.05mm continuum peak of MM1,
$\mathrm{N}(\mathrm{CH}_{3}\mathrm{OH})=(2.22\pm0.01)\times10^{18}$cm$^{-2}$
and $T_{\mathrm{ex}} = 162.7\substack{+0.3 \\ -0.5}$K based on pixel-by-pixel
Bayesian analysis of LTE synthetic methanol spectra across MM1. Intriguingly,
the peak CH$_{3}$OH $T_{\mathrm{ex}}=165.5\pm0.6$ K is offset from MM1's
millimetre continuum peak by $0.22''\sim880$au, and a region of elevated
CH$_{3}$OH $T_{\mathrm{ex}}$ coincides with free-free VLA 5.01cm continuum,
adding to the tentative evidence for a possible unresolved high-mass binary in
MM1. In our VLA 1.21cm data, we report the first NH$_{3}$(3,3) maser detections
towards G19.01$-$0.03, along with candidate 25GHz CH$_{3}$OH $5(2,3)-5(1,4)$
maser emission; both are spatially and kinematically coincident with 44GHz
Class I CH$_{3}$OH masers in the MM1 outflow. We also report the ALMA detection
of candidate 278.3GHz Class I CH$_{3}$OH maser emission towards this outflow,
strengthening the connection of these three maser types to MYSO outflows.
