  We theoretically address the effects of strong magnetic fields in
three-dimensional Weyl semimetals (WSMs) built out of Weyl nodes with a
monopole charge $n$. For $n=1$, $2$, and $3$ we realize single, double, and
triple WSM, respectively, and the monopole charge $n$ determines the integer
topological invariant of the WSM. Within the linearized continuum description,
the quasiparticle spectrum is then composed of Landau levels (LLs), containing
exactly $n$ number of chiral zeroth Landau levels (ZLLs), irrespective of the
orientation of the magnetic field. In the presence of strong backscattering,
for example, (due to quenched disorder associated with random impurities),
these systems generically give rise to longitudinal magnetotransport.
Restricting ourselves to the quantum limit (and assuming only the subspace of
the ZLLs to be partially filled) and mainly accounting for Gaussian impurities,
we show that the longitudinal magnetoconductivity (LMC) in all members of the
Weyl family displays a positive linear-$B$ scaling, when the field is applied
along the axis that separates the Weyl nodes. But, in double and triple WSM,
LMC displays a smooth crossover to a nonlinear $B$-dependence as the field is
tilted away from such a high-symmetry direction. In addition, due to the
enhanced density of states, the LL quantization can trigger instabilities
toward the formation of translational symmetry breaking density-wave orderings
for sufficiently weak interaction (BCS instability), which gaps out the ZLLs.
Concomitantly as the temperature (magnetic field) is gradually decreased
(increased) the LMC becomes negative. Thus WSMs with arbitrary monopole charge
($n$) can host an intriguing interplay of LL quantization, longitudinal
magnetotransport (a possible manifestation of one-dimensional chiral or axial
anomaly), and density-wave ordering, when placed in a strong magnetic field.
