When new members join a LIVE group, they will be emailed all the modules that have already been released to the group. They can also log in to their client portal and click on “Modules”.
If your group is EVERGREEN, members will receive all modules according to the release schedule you set up regardless of when they join the group.
However, if you set your group to be "self-paced", your new members don't have to wait for the next module to arrive. They can simply unlock the next module by marking the previous one as completed.