${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ and ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ are antiferromagnetic topological insulators belonging to the ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$ series, where structural layering provides a natural route to tune magnetic interaction in van der Waals magnets. Despite extensive interest in their topological properties, how the insertion of ${\mathrm{Bi}}_2{\mathrm{Te}}_3$ quintuple layers modifies magnetic critical fluctuations near the antiferromagnetic transition remains unresolved. Here, we combine scanning tunneling microscopy (STM), critical scaling analysis and magnetocaloric measurements to directly correlate real-space structures with magnetic criticality. STM reveals atomically flat septuple-layer terraces in ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, whereas ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ displays coexisting septuple and quintuple-layer terminations reflecting its alternating stacking sequence. ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ exhibits robust three-dimensional Ising-like critical behavior together with a distinct low-temperature first-order transition. In contrast, ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ displays crossover-dominated criticality arising from weakened interlayer exchange and competing magnetic phases. Correspondingly, the magnetocaloric response differs significantly between the two compounds. ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ shows dual-type magnetocaloric behavior with a sharp field-induced sign reversal of the isothermal magnetic entropy change ($-\mathrm{\Delta }{S}_M$). It exhibits both inverse ($-\mathrm{\Delta }{S}_M<0$) and conventional ($-\mathrm{\Delta }{S}_M>0$) magnetocaloric effects. In contrast, ${\mathrm{MnBi}}_4{\mathrm{Te}}_7$ shows only conventional magnetocaloric response with a broad positive entropy peak. These results establish structural layering as a key parameter governing magnetic critical fluctuations and magnetocaloric behavior in ${\mathrm{MnBi}}_{2n}{\mathrm{Te}}_{3n+1}$ topological magnets.

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• Critical field
• Magnetism
• Magnetocaloric effect