It is proved that two-dimensional spin-l/2 XYZ models can be mapped onto generalized Ashkin-Teller models, in the first approximation of a realization of the decomposition scheme proposed by Suzuki. Consequently, it is shown that a large class of quantum spin models can be investigated analytically within the present approximation. Some analytic and numerical results are explicitly obtained with respect to thermal and critical properties in some interesting cases. It is also pointed out that the present mapping suggests a procedure to overcome the well-known negative sign problem in performing Monte Carlo calculations of frustrated quantum spin models.