Development of a [229]Th nuclear optical clock requires precise and model-insensitive nuclearstructure parameters, which presently suffer from limited accuracy and poor consistency. We propose a joint spectroscopy scheme using two highly charged [229]Th ions with J = 1/2 electronic ground states, where the lowest electronic excitation energy of each ion far exceeds the nuclear transition energy. This configuration effectively forms a three-level system comprising the electronic ground state and the nuclear ground (g) and isomeric (m) states, resulting in strongly enhanced nuclear hyperfine mixing. Within this framework, a unified analysis of precision measurements on both ions enables the simultaneous determination of five key nuclear parameters without relying on external nuclear inputs: the magnetic dipole moments µg and µm, the bare-nucleus transition energy ωn, the charge-radius difference δ⟨r[2]⟩gm, and the M1 transition matrix element TM1. With this approach, the uncertainties in ωn and δ⟨r[2]⟩gm are estimated to be reduced by factors of 3 and 2, respectively, compared with current values. This work could provide a useful benchmark for nuclear theory and serve as a foundation for future development of a [229]Th-based nuclear optical clock.