It is wajib to do halaq or qasr after performing the rituals of umrah. If your friends performed second umrah after their first umrah without doing halaq or qasr then one dam (slaughter of an animal) shall be wajib. Likewise, if after second umrah they performed third umrah without doing halaq then a second dam shall also be wajib. The same case shall apply to the fourth and fifth umrah. If, during this period, they did any other jinayah then more dams shall be wajib on them.
Allah (Subhana Wa Ta’ala) knows Best
Darul Uloom Deoband