The best thing you can do is help them break the project into smaller, manageable chunks rather than letting it feel like one giant overwhelming thing - that alone usually cuts the anxiety in half. You could also coach them on having a quick conversation with their groupmates about dividing tasks more fairly, or talking to the teacher if things genuinely aren't working (most teachers appreciate hearing about this stuff early). In the meantime, make sure they're taking breaks, getting outside a bit, and not letting this one project consume every evening - perspective matters when you're stressed. The work they're doing now is actually more valuable than a perfect grade, because they're learning how to handle unfair situations, which is something they'll deal with forever.