Infall motion and mass evolution of groups A (left panel) and B (right panel) towards the cluster pair. Upper panels: redshift evolution of the alignment between radial direction towards the pair (centre of mass, blue; GC1, red; GC2; yellow) and subhalo velocity (as in the legend), quantified by the cosine of the angle between them. For Group B (right), the gas < R₅₀₀ at z = 0.16 is tracked to lower redshifts after entering the GC1 virial boundary. Lower panels: redshift evolution of the subhalo DM (solid lines) and gas (dashed lines) bound mass.