If a group of girls is already traveling to Saudi without a Mahram, what is the ruling for them to do Umrah? They are travelling anyways for sightseeing.
بِسْمِ اللهِ الرَّحْمنِ الرَّحِيْم
In the name of Allah, the Most Gracious, the Most Merciful
Umrah is a sacred act of worship. It should be done in accordance with how Shariah wants us to do it. Abdullah ibn Umar (r) narrates that the Messenger of Allah (saw) said: “A woman must not travel for three days except with a Mahram.” Even if a woman goes in the state of Ihram without her husband or Mahram, she will be Muhsarah (confined from finishing the Umrah).
Therefore, it would not be permissible for a group of girls to travel to Saudi Arabia without a Mahram and perform Umrah.
Only Allah knows best
Written by Maulana Mohammed Kamran Abid
Checked and approved by Mufti Mohammed Tosir Miah
Darul Ifta Birmingham
 Sahih al-Bukhari, Hadith# 1087
 Al-Fatawa Al-Hindiya, vol. 1, pg. 255, Darul Fikr