The discontinuous order-disorder structural instabilities occurring in TEA₂BCl₄ with B = Zn, Cu, Hg are studied by means of X-ray diffraction, polarized light microscopy, and from the point of view of symmetry. The sequence of phases is clarified but there remains ambiguity concerning symmetry and structure of some phases. Kinetic phenomena and unexpected residual inhomogeneity are observed in paraelastic phases after passing the ferroelastic transition.