How to grade unequal contributions to group work as a TA bound by instructor's rules
I suggest that you grade &quot;the project&quot; for its value and assign every student the same grade. If any student objects, refer them to the instructor. This recognizes an important fact.
You may not recognize all &quot;contributions&quot;, but the students might value some things more than others. Not every student needs to contribute to a &quot;team&quot; project in the same way. The same is true for real world projects.
If you try to change things or devise some &quot;scheme&quot;, then you will be the bad person, disrespected by everyone.
The work is the work. Grade it.

I actually think that &quot;dividing up&quot; the work makes it harder since the integration adds another step. I think that the so called &quot;best&quot; students do everyone a disservice if they do all the work. But if I give a project to a team and don't instruct them otherwise on process, then the team process is up to them. Respect that.

I gave a lot of team projects. One thing I did was have peer evaluations of the form &quot;Who were the two most helpful members of your team and why&quot;. That would be for a team of four or so. I once had the experience that the team was unanimous in praising one person who I thought was slacking because their contributions weren't visible to me. But he actually kept the team functioning and moving forward. It may be that you wouldn't want to hire him for is technical skills, but you almost certainly would as a manager of a technical team. But that is mere supposition on my part, so don't read too much in to it.
Don't expect every student to learn exactly the same thing from a course.
I once had another student in a class who I predicted would eventually be the manager of all the &quot;geeks&quot; since she asked the right questions. She focused more on &quot;why&quot; instead of &quot;how&quot;. There are a lot of skills.