Praise be to Allah.
What every Muslim must do is learn what he needs to know about his religion so that his belief and worship will be correct. This is what the Prophet (blessings and peace of Allah be upon him) instructed his companions to do, during the Hajj that he performed with the people. He said to them: “Learn from me your rituals (of Hajj), for I do not know, perhaps I will not perform Hajj again after this Hajj of mine.” Narrated by Muslim (1297)
An-Nawawi (may Allah have mercy on him) said:
This is an instruction, and what is meant is that these things that I have done during my pilgrimage of words, actions and ways of doing things are how Hajj is to be done, and they are your rituals, so learn them from me, accept them and keep them in mind; learn them and teach them to the people.
It was said to Imam Ahmad: Is seeking knowledge obligatory?
He said: Yes, about your religion; whatever you need to know, you should learn it.
He also said:
It is obligatory for him to seek knowledge of whatever will help him to practice his religion and he should not be negligent concerning it.
He was asked: Must he learn all the knowledge he needs in order to practice his religion?
He said: He should learn obligatory matters that he himself is required to do. He has no choice but to seek knowledge of them.
He was asked: Such as what?
He said: Whatever he cannot afford not to know such as prayer, fasting and so on.
Al-Adab ash-Shar‘iyyah by Ibn Muflih (2/99-100)
As your parents did more laps due to their ignorance of the ruling, their ‘umrah is valid. They did the seven laps of sa‘i that are required, and whatever was surplus to that is not counted and there is no ruling concerning it.
Shaykh Ibn Baaz (may Allah have mercy on him) was asked:
I did sa‘i between as-Safa and al-Marwah, but I did each lap on the basis that going from as-Safa and back to as-Safa was one lap. Do I have to do offer any compensation for that?
The Shaykh replied:
This was something extra that you did. You did fourteen laps when what is required is seven, so the other seven do not count, because they were contrary to what is required by Islamic teaching. You are excused because of your ignorance, but you have to repent to Allah from that, and not do that again if you go for Hajj or ‘umrah, because you did what was required of seven laps, from as-Safa to al-Marwah, then from al-Marwah to as-Safa, starting with as-Safa and ending with al-Marwah, seven laps. End quote.
Majmoo‘ Fataawa Ibn Baaz (17/341-342)
See: Fataawa ash-Shaykh Ibn ‘Uthaymeen (22/424)
For a description of ‘umrah please see the answer to question no. 31819
And Allah knows best.