I am afraid that their Hajj and Umrah will be rejected by Allah because of their sins.
The Common Mistakes/Sins during Hajj and Umrah are as follow.
Passing in Front of a Person Who is Praying (shalat)
Many people passing in front of a person who is praying (shalat). Especially when they try to reach Raudhoh or Kaaba or going back to their place. The sin is very big:
that Zaid bin Khalid sent him to Abi Juhaim to ask him what he had heard from Allah's Apostle about a person passing in front of another person who was praying. Abu Juhaim replied, "Allah's Apostle said, 'If the person who passes in front of another person in prayer knew the magnitude of his sin he would prefer to wait for 40 (days, months or years) rather than to pass in front of him." Abu An-Nadr said, "I do not remember exactly whether he said 40 days, months or years."
It's better we pass behind rather than in front of praying people. Or pass 1-2 shaf in front of him or just wait until he finish his prayer.
Abu al-Waddak said: "A young person tried to pass in front of Abu Sa'id while he was praying. Abu Sa'id held him off and then the young man tried again. Abu Sa'id pushed him off. This happened three times and when [Abu Sa'id] finished [the prayer], he said: 'The salah is not invalidated by anything but the Messenger of Allah said: 'Repulse [the person who is trying to pass in front of you] to the best of your ability for he is a devil.'" [Abu Dawud]
The Prophet said, "If while you are praying, somebody intends to pass in front of you, prevent him; and should he insist, prevent him again; and if he insists again, fight with him (i.e. prevent him violently e.g. pushing him violently), because such a person is (like) a devil." [Bukhari 4.495]
Abu Saleh as-Saman said: "I will narrate to you what I heard and saw from Abu Sa'id al-Khudri. One day I was with Abu Sa'id and he was offering salah on Friday facing something which concealed him from the people when a young man from the tribe of Mu'ait came and tried to pass in front of Abu Sa'id. He pushed him back. He tried again and Abu Sa'id struck him harder. The two scuffled. The man went to Marwan to complain. Abu Sa'id also went to Marwan. Marwan asked: 'What has happened between you and the son of your brother that caused him to complain?' Abu Sa'id said: 'I heard the Prophet say: 'If any of you prays toward a sutrah and someone tries to pass in front of you, then turn him away. If he refuses, use force for he is a devil."' [Bukhari and Muslim]
Haste and Disturb Other Pilgrim
Many people haste and disturb other pilgrim. Sometimes the haste kill many pilgrims such as happen in Mina Tunnel which caused 1,426 Muslims died in human stampede.
"Haste is an evil deed", that's what the Prophet Muhammad in Tirmidzi hadeeth.
Just look at wikipedia article:
Sometimes the surging crowds, trekking from one station of the pilgrimage to the next, cause a stampede. Panic spreads, pilgrims jostle to avoid being trampled, and hundreds of deaths can result. The Stoning of the Devil ceremony is particularly crowded and dangerous.
Plains of Arafat on the day of Hajj
July 2, 1990 : A stampede inside a pedestrian tunnel (Al-Ma'aisim tunnel) leading out from Mecca towards Mina, Saudi Arabia and the Plains of Arafat led to the deaths of 1,426 pilgrims.
May 23, 1994 : A stampede killed at least 270 pilgrims at the stoning of the Devil ritual.
April 9, 1998: at least 118 pilgrims were trampled to death and 180 injured in an incident on Jamarat Bridge.
March 5, 2001: Thirty five pilgrims were trampled to death in a stampede during the stoning of the Devil ritual.
February 11, 2003: The stoning of the Devil ritual claimed 14 pilgrims' lives.
February 1, 2004: 251 pilgrims were killed and another 244 injured in a stampede during the stoning ritual in Mina.
Wikinews has related news: Hundreds dead in Hajj stampede
January 12, 2006: A stampede during the ritual ramy al-jamarāt on the last day of the Hajj in Mina killed at least 346 pilgrims and injured at least 289 more. The incident occurred shortly after 13:00 local time, when a busload of travellers arrived together at the eastern access ramps to the Jamarat Bridge. This caused pilgrims to trip, rapidly resulting in a lethal crush. An estimated two million people were performing the ritual at the time.
Be patient because Allah loves people who is patient... (Quran 2:3)