Some of my thoughts: you would use jullie/jullie if you want to be explicit that you are referring something of the group, not just the individual: Jullie moeten jullie afval opruimen refers to the trash of the group, not just your own trash.
If you don't want to be that explicit, you use 'je' in the second part of the sentence.
I think this is the best explanation for why we would use jullie/je: https://taaladvies.net/jullie-of-je-tassen/
Some of my thoughts: you would use jullie/jullie if you want to be explicit that you are referring something of the group, not just the individual: Jullie moeten jullie afval opruimen refers to the trash of the group, not just your own trash. If you don't want to be that explicit, you use 'je' in the second part of the sentence.