We study the coupled twin-diamond chain, a decorated one-dimensional Ising model motivated by the magnetic structure of ${\mathrm{Cu}}_2{\left({\mathrm{TeO}}_3\right)}_2{\mathrm{Br}}_2$. By applying an exact mapping to an effective Ising chain, we obtain the full thermodynamic description of the system through a compact transfer-matrix formulation. The ground-state analysis reveals five distinct phases, including two frustrated sectors with extensive degeneracy. These frustrated regions give rise to characteristic entropy plateaus and separate the ordered phases in the zero-temperature diagram. At low temperatures the model exhibits peculiar sharp yet continuous variations of entropy, magnetization, and response functions, reflecting clear signatures of pseudotransition behavior. The coupled twin-diamond chain thus provides an exactly solvable setting in which competing local configurations and internal frustration lead to pronounced dual pseudocritical features in one dimension.

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• Frustrated magnetism
• Phase transitions
• 1-dimensional spin chains
• Transfer matrix method