Can I export everyone's grade report at the same time?

You sure can. Go to Academics > Courses. If all of the courses have been finalized, click Export and select Grade Reports. Select a Program and click Export. All of the relevant grade reports will print as one, single PDF document.

Of course, students who don't have a Grade/Transcript Lock can get their own grade reports from their profiles any time after their courses for the Term are finalized.