To add to my previous answer (and to reply to your comment), the set of equations for Pareto optimality include the MRS equations and the feasibility equations.
MRS equations: \begin{align} \text{MRS}^A_{x,y} = \text{MRS}^B_{x,y} = \text{MRS}^C_{x,y} &\iff \frac{\frac{\partial U_A}{\partial x}}{\frac{\partial U_A}{\partial y}} = \frac{\frac{\partial U_B}{\partial x}}{\frac{\partial U_B}{\partial y}} = \frac{\frac{\partial U_C}{\partial x}}{\frac{\partial U_C}{\partial y}} \\ &\iff \frac{y_A z_A^2}{x_A z_A^2} = \frac{2x_By_Bz_B}{x_B^2z_B} = \frac{y_C^2z_C}{x_Cy_Cz_C} \tag{1} \\ \text{MRS}^A_{y,z} = \text{MRS}^B_{y,z} = \text{MRS}^C_{y,z} &\iff \frac{\frac{\partial U_A}{\partial y}}{\frac{\partial U_A}{\partial z}} = \frac{\frac{\partial U_B}{\partial y}}{\frac{\partial U_B}{\partial z}} = \frac{\frac{\partial U_C}{\partial y}}{\frac{\partial U_C}{\partial z}}\tag{2} \\ \text{MRS}^A_{z,x} = \text{MRS}^B_{z,x} = \text{MRS}^C_{z,x} &\iff \frac{\frac{\partial U_A}{\partial z}}{\frac{\partial U_A}{\partial x}} = \frac{\frac{\partial U_B}{\partial z}}{\frac{\partial U_B}{\partial x}} = \frac{\frac{\partial U_C}{\partial z}}{\frac{\partial U_C}{\partial x}} \tag{3} \end{align}
The feasibility allocations are: $$x_A + y_A + z_A = 1 + 2 + 1 = 4 \tag{4}$$ $$x_B + y_B + z_B = 1 + 1 + 5 = 7 \tag{5}$$ $$x_C + y_C + z_C = 1 + 3 + 1 = 5 \tag{6}$$
The equations $1-6$ combined will give you the final Pareto Efficient allocations.