When setting up a critique is vital that it stays contained and focused on the work. You may want to start by asking the creators to provide contextual information to the reviewers, such as their intent, who their audience was, and what constraints and choices they made. It is also worthwhile setting goals and intentions for the reviewers too - what are they expected to comment on, what is out of bounds, and what they can provide suggestions or instructions. Some of the most valuable critiques are necessarily the judgements, but questions back to the student about their work. Get reviewers to focus feedback on addressing the intent and goals of the work and how effective they were in addressing them.