Is ok to have boxes of raw chicken stacked on top of each other
This should be fine if there is no other food below the chicken wings. What you don't want is for the chicken to be in a position to contaminate other foods.
General food service guide lines include:

From "Preventing Cross-Contamination During Storage Fact Sheet" (appears to originally be from the National Restaurant Educational Foundation, hosted here by New York's National Guard food service):


  Store raw meat, poultry and fish separately from prepared and ready-to-eat food. If these items cannot be stored separately, store them below prepared or ready-to-eat food. Raw meat, poultry and fish should be stored in the following [order (top to bottom)]: whole fish, whole cuts of beef and pork, ground meats and fish, and whole and ground poultry.