  The two-band/two-gap superconductivity in aluminium and carbon doped MgB$_2$
has been addressed by the point-contact spectroscopy. Two gaps are preserved in
all samples with $T_c's$ down to 22 K. The evolution of two gaps as a function
of the critical temperature in the doped systems suggest the dominance of the
band-filling effects but for the increased Al-doping the enhanced interband
scattering approaching two gaps must be considered. The magnetic field
dependences of the Andreev reflection excess currents as well as zero-energy
density of states determined from the experimental data are used to analyze the
intraband scattering. It is shown, that while the C-doping increases the
intraband scattering in the $\pi$-band more rapidly then in the $\sigma$ band,
the Al-doping does not change their relative weight.
