To reach the concentration phase boundary between antiferromagnetic Cu₂GaBO₅ and ferrimagnetic Cu₂MnBO₅ ludwigites, solid solutions Cu₂Mn_1−xGa_xBO₅ (x = 0.05, 0.1, 0.15, 0.175) were grown by the flux technique using a multi-component solvent based on Bi₂Mo₃O₁₂ with the addition of Na₂B₄O₇ which significantly influenced the crystal formation and cation composition of the studied compounds. The content of the flux system was corrected taking into account the earlier established relationship of the partition coefficients of Mn₂O₃ and Ga₂O₃. The influence of the solvent components on the ludwigite crystallization was analyzed. The maximum size of the grown crystal was 1 × 1 × 4 mm³. The structure and cation composition of the grown compounds were studied using X-ray (X-ray diffraction, EDX (energy-dispersive X-ray spectroscopy)) and vibrational (Raman) spectroscopy techniques. The phase boundary of Cu₂MnBO₅-Cu₂GaBO₅ was found to be in the concentration range of x = 0.15-0.175, corresponding to a change in the monoclinic axis direction and a leap in the lattice parameters. The symmetry evolution of metal-oxygen octahedra for four nonequivalent cation positions was analyzed, and the unique crystal structure of Cu₂MnBO₅ demonstrated high rigidity relative to the introduction of Ga³⁺ cations. The polarized Raman spectra of monoclinic ludwigites were obtained and studied for the first time. A comparison of the spectra of the studied samples in both phases and orthorhombic ludwigites was made. A number of spectral features due to the monoclinic distortions in the crystal were found. In agreement with the Raman experiment, the concentration phase boundary was close to 0.15.