The recently developed macroscopic model of light-induced equilibrium of spin-crossover solids is extended to the case of two equivalent sublattices coupled `antiferromagnetically'. To do this, we use an Ising-like model involving two coupling parameters of opposite signs for the intra- and inter-sublattice interactions, previously introduced to describe the two-step static spin transition, and we have adapted the macroscopic master equation describing the time evolution of the system accordingly. We mostly report on the quasi-static solutions of the system, under constant light irradiation and for slow temperature variations. Light-induced thermal hysteresis loops are obtained and have typical two-step shapes for suitable sets of parameter values. The model predicts, in analogy with the static transition, a possible light-induced symmetry breaking between the structurally equivalent sublattices. Kinetic effects are briefly described.