When assigning a task to a group, it is not user-friendly for the assignees to mark the task as complete. There are many steps to checking off the task, and it seems like you're doing it the wrong way when really it's the right way. Additionally, one assignee is able to mark a task as complete on behalf of another assignee, which usually happens by accident. When an assignee opens a task that has been assigned to a group of people, they should be able to easily mark it as complete or incomplete for themselves only. The way it is right now seems very incomplete as it's open to a lot of manipulation. Additionally, it would be nice to have a completion percentage within the task so that if 10 of 20 users marked it as complete, then it would show 50% done, for example.