  We show that the magnetic and vacancy orders in the 122
$(A_{1-y}Fe_{2-x}Se_2)$ iron-chalcogenides can be naturally derived from the
$J_1-J_2-J_3$ model with $J_1$ being the ferromagnetic (FM) nearest neighbor
exchange coupling and $J_{2}, J_3$ being the antiferromagnetic (AFM) next and
third nearest neighbor ones respectively, previously proposed to describe the
magnetism in the 11(FeTe/Se) systems. In the 11 systems, the magnetic exchange
couplings are extremely frustrated in the ordered bi-collinear
antiferromagnetic state so that the magnetic transition temperature is low. In
the 122 systems, the formation of iron vacancy order reduces the magnetic
frustration and significantly increases the magnetic transition temperature and
the ordered magnetic moment. The pattern of the 245 iron-vacancy order
($\sqrt{5}\times \sqrt{5}$) observed in experiments is correlated to the
maximum reduction of magnetic frustration. The nature of the iron-vacancy
ordering may hence be electronically driven. We explore other possible vacancy
patterns and magnetic orders associated with them. We also calculate the spin
wave excitations and their novel features to test our model.
