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We present theoretical study on quantum tunnelling in n-coupled single-molecule magnets (SMMs) by spincoherent-state path integral. It is found that, due to weak coupling between SMMs, the tunnelling process involving more than one-spin-flip is effectively blocked and the main contribution to the relaxation of the magnetization comes from the tunnelling processes involving just one-spin-flip. Starting from the negative saturated magnetization, the effect of the antiferromagnetic on tunnelling coupling is found to be qualitatively different from the ferromagnetic coupling. A criterion is developed to determine both the nature and the strength of the exchange coupling from the position of the first resonance of a spherical sample with homogeneous magnetization.