We report the synthesis and comprehensive investigation of ${\mathrm{Cu}}_{1-x}{\mathrm{Cr}}_{1-x}{\mathrm{Co}}_{2x}{\mathrm{P}}_2{\mathrm{S}}_6$ (CCCPS) single crystals and powder samples, a substituted derivative of the van der Waals multiferroic ${\mathrm{CuCrP}}_2{\mathrm{S}}_6$ (CCPS) where ${\mathrm{Co}}^{2+}$ ions simultaneously substitute for $\mathrm{C}{\mathrm{u}}^{+}$ and $\mathrm{C}{\mathrm{r}}^{3+}$. Through structural and magnetic structure determination, magnetometry measurement, pyroelectric and magnetodielectric (MD) probes, we map a substitution-controlled crossover from a CCPS-like to a ${\mathrm{CoPS}}_3$ (CPS)-like regime. Co substitution rapidly suppresses long-range antiferroelectric (AFE) ordering (C2/c→Pc) of CCPS at $\sim 150\mathrm{K}$ for $\mathrm{x}\ge 0.2$, leaving short-range polar fluctuations to persist. Moreover, a structural transformation from the C2/c phase to the C2/m phase occuring near $x\approx 0.35$ is observed. In the low-substitution C2/c phase $(0.1\le x\le 0.3)$, multiple field-induced spin-flop transitions are observed, which are subtle in magnetization but pronounced in the MD response, revealing the strong coupling between spin orientation and residual polar dynamics. A double spin-flop behavior is ascribed to the synergistic effect between the strong single-ion anisotropy of $\mathrm{C}{\mathrm{o}}^{2+}$ in the low-symmetry C2/c crystal field and newly introduced antiferromagnetic (AFM) exchange interactions within the Cr triangular lattice. For intermediate substitution levels $(0.4\le x\le 0.6)$, a hybrid magnetic state emerges, characterized by a ferromagnetic component superimposed on a zigzag AFM background. In the high-substitution limit, the system converges with the zigzag antiferromagnet order of ${\mathrm{CoPS}}_3$. Our results reveal a rich interplay between lattice symmetry, competing magnetic interactions, and residual polar dynamics, offering a versatile strategy for engineering multiple spin-reorientation phases and enhanced magnetoelectric (ME) coupling in two-dimensional van der Waals thiophosphates.

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• Dielectric properties
• Magnetic anisotropy
• Magnetic order
• Magnetic phase transitions
• Magnetoelectric effect
• Structural phase transition
• Crystal structures
• Multiferroics
• van der Waals systems
• Dielectric constant measurements
• Magnetization measurements
• Raman spectroscopy
• Susceptibility measurements
• X-ray diffraction