  Neutron star (NS) binaries can be potentially intriguing gravitational wave
(GW) sources, with both high- and low-frequency radiations from the possibly
aspherical individual stars and the binary orbit, respectively. The successful
detection of such a dual-line source could provide fresh insights into binary
geometry and NS physics. In the absence of electromagnetic observations, we
develop a strategy for inferring the spin-orbit misalignment angle using the
tight dual-line double NS system under the spin-orbit coupling. Based on the
four-year joint detection of a typical dual-line system with LISA and Cosmic
Explorer, we find that the misalignment angle and the NS moment of inertia can
be measured with sub-percentage and 5% accuracy, respectively.
