This is the 6082nd most frequent Arabic word.
وعليهم
"And upon them."
Here, "وعليهم" translates to "and they must," where "و" means "and" and "عليهم" conveys obligation for the subject.
وعليهم أن ينجزوا الواجب قبل الموعد النهائي.
They must complete the assignment before the deadline.
In this context, "وعليهم" is used to indicate that it is a responsibility or requirement for them to discuss.
طلب الأستاذ من الجميع الاستماع، وعليهم الآن المناقشة.
The teacher asked everyone to listen, and now they must discuss.
Here, "وعليهم" suggests an obligation or a necessity for the subjects to perform the act of thinking.