  The ground-based gravitational wave (GW) observatories discover a population
of merging stellar binary black holes (BBHs), which are promising targets for
multiband observations by the low-, middle-, and high-frequency GW detectors.
In this paper, we investigate the multiband GW detections of BBHs and
demonstrate the advantages of such observations in improving the localization
and parameter estimates of the sources. We generate mock samples of BBHs by
considering different formation models as well as the merger rate density
constrained by the current observations (GWTC-3). We specifically consider the
astrodynamical middle-frequency interferometer GW observatory (AMIGO) in the
middle-frequency band and estimate that it may detect $21$-$91$ BBHs with
signal-to-noise ratio $\varrho\geq8$ in a $4$-yr observation period. The
multiband observations by the low-frequency detectors [Laser Interferometer
Space Antenna (LISA) and Taiji] and AMIGO may detect $5$-$33$ BBHs with
$\varrho_{\rm LT}\geq5$ and $\varrho_{\rm AMI}\geq5$, which can evolve to the
high-frequency band within $4$ yr and can be detected by the Cosmic Explorer
(CE) and Einstein Telescope (ET). The joint observations of
LISA-Taiji-AMIGO-ET-CE may localize the majority of the detectable BBHs in sky
areas of $7\times10^{-7}$ to $2\times10^{-3}$ deg$^2$, which is improved by a
factor of $\sim120$, $\sim2.4\times10^{5}$, $\sim1.8\times10^{4}$, or
$\sim1.2\times10^{4}$, comparing with those by only adopting CE-ET, AMIGO,
LISA-Taiji, or LISA-Taiji-AMIGO. These joint observations can also lead to an
improvement of the measurement precision of the chirp mass (symmetric mass
ratio) by a factor of $\sim5.5\times10^{4}$ ($33$), $\sim16$ ($8$), $\sim120$
($90$), or $\sim5$ ($5$), comparing with those by CE-ET, AMIGO, LISA-Taiji, or
LISA-Taiji-AMIGO.
