Lanthanum polyhydrides, synthesized under extreme pressure, exhibit near-room-temperature superconductivity. Finding a precise arrangement of the hydrogen sublattice that is critical for understanding the strong electron-phonon coupling remains experimentally unresolved due to the small X-ray scattering form factor of hydrogen atoms. In this work, we attempt to computationally reconstruct hydrogen sublattices of the LaH₁₂ at 100-200 GPa combining unconstrained evolutionary searches and structure generation with fixed lanthanum sublattice. By implementing a similarity metric, we screen the computationally generated configurations against experimental powder X-ray diffraction data. We specifically identify the trigonal R3̄-LaH₁₂ and pseudo-hexagonal C222₁-La₂H₂₄ phases, which demonstrate close agreement with the experimental X-ray diffraction data. First-principles calculations confirm the metallic and superconducting nature of these hydrides. Crucially, our lattice dynamics analysis using the stochastic self-consistent harmonic approximation (SSCHA) indicates that these structures are dynamically stable. We reveal the presence of molecular H₂ units and soft phonon modes in the trigonal LaH₁₂ that suppresses superconductivity (T_c ≥ 30 K), while the hydrogen clathrate network in the C222₁ phase drives strong electron-phonon interactions, yielding the coupling parameters of λ≈ 1.83, ω_log ≈ 87.5 meV and transition temperature of T_c≈ 150 K at 150 GPa.