It appears that there are still one or two students who haven't joined a project group. Since two (or even three) people aren't enough to support the workload of this project, these students will need to join groups that have already formed.

If you are a member of such a group and get a request to join your group from one of these students, please do your best to accommodate them.

Minimum number for a group is 4, but you can have 5 or 6 if necessary. Beyond 6 gets unwieldy for group meetings and whatnot, but 5 or 6 is usually doable.