I didn't fully understand what I was talking about when I replied, and for that I apologize. Now that I know a little bit more, this is basically how it works (I think):

We cannot see posts made directly on Mastodon. However, they can see posts made on Lemmy and even comment on them. We are able to see those comments as normal and without doing anything on our end, but again, that's only as long as they're made under Lemmy posts