The van der Waals magnets ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ and ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$, chemically similar yet magnetically distinct, provide an ideal platform for probing how structural complexity governs emergent magnetic order, anisotropy, and topological textures. ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ does not host skyrmions, whereas ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ does, raising fundamental questions about the roles of inversion symmetry, frustration, and exchange interactions. Through comprehensive magnetization, susceptibility, and critical exponent analysis, we demonstrate that magnetic frustration, absent in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$, is crucial in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$. The extra ${\mathrm{Fe}}^{+}$ sublattice in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ breaks inversion symmetry, introduces competing exchange, and yields a significant frustration parameter $f\approx$ 3.8. Critical exponent analysis reveals field-driven crossover from a mean field to a 2D-Heisenberg class with increasing field in ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$, whereas field-driven crossover from a frustrated 3D-Heisenberg class ($\beta =0.348,\gamma =1.32$) at low fields reveals a conventional 3D-Heisenberg class ($\beta =0.368,\gamma =1.368$) at high fields in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$. Our results establish magnetic frustration, rather than the Dzyaloshinskii-Moriya interaction alone, as the key ingredient stabilizing skyrmionic phases, offering a design principle for topological spin textures in layered van der Waals magnets. We show here that an extra sublattice in ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$ is essentially responsible for most of the differences in magnetic properties between ${\mathrm{Fe}}_3{\mathrm{GeTe}}_2$ and ${\mathrm{Fe}}_5{\mathrm{GeTe}}_2$.

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• Magnetic anisotropy
• Magnetic coupling
• Magnetic interactions
• Magnetic order
• Magnetic phase transitions
• Magnetic susceptibility
• Magnetization dynamics
• Spin dynamics
• Spin-orbit coupling