We use the Fisher information matrix to investigate the angular resolution and luminosity distance uncertainty for coalescing binary neutron stars (BNSs) and neutron star-black hole binaries (NSBHs) detected by the third-generation (3G) gravitational-wave (GW) detectors. Our study focuses on an individual 3G detector and a network of up to four 3G detectors at different locations including the US, Europe, China and Australia for the proposed Einstein Telescope (ET) and Cosmic Explorer (CE) detectors. We in particular examine the effect of the Earths rotation, as GW signals from BNS and low mass NSBH systems could be hours long for 3G detectors. We find that, a time-dependent antenna beam-pattern function can help better localize BNS and NSBH sources, especially those edge-on ones. The medium angular resolution for one ET-D detector is around 150 deg$^2$ for BNSs at a redshift of $z=0.1$. The medium angular resolution for a network of two CE detectors in the US and Europe respectively is around 20 deg$^2$ at $z=0.2$ for the simulated BNS and NSBH samples. While for a network of two ET-D detectors, the similar angular resolution can be achieved at a much higher redshift of $z=0.5$. The angular resolution of a network of three detectors is mainly determined by the baselines between detectors regardless of the CE or ET detector type. We discuss the implications of our results to constrain the Hubble constant $H_0$, the deceleration parameter $q_0$ and the equation-of-state (EoS) of dark energy. We find that in general, if 10 BNSs or NSBHs at $z=0.1$ with known redshifts are detected, $H_0$ can be measured with an accuracy of $0.9%$. If 1000 face-on BNSs at $z<2$ are detected with known redshifts, we are able to achieve $Delta q_0=0.002$, or $Delta w_0=0.03$ and $Delta w_a=0.2$ for dark energy.(Abridged version).
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