Can We Enter Makkah without Ihram?
Question

My wife and I went to do `Umrah a few years ago; we went with another family in their car from Riyadh. My friend said to us that it was possible for us to enter Makkah al-Mukarramah without ihram and stay there overnight, then enter ihram from there. So we did that, without knowing that this was something prohibited. That `Umrah was not the obligatory `Umrah. We have also done `Umrah many times since then, entering ihram from the miqat.
Do we have to do anything with regard to that `Umrah?
If we have to offer a sacrifice, are there any organizations that can do that on our behalf, because I am working in Riyadh?
Praise be to Allah.Can we enter Makkah without ihram?
Your friend undoubtedly made a mistake when he told you it was permissible to pass the miqat without entering ihram, and he made another mistake when he made you enter ihram from Makkah itself, because the people of Makkah and those who come under the same ruling as them must go outside the boundary of the Haram zone (to enter ihram) if they want to do `umrah. 
Islam has defined the miqats for those who come to Makkah for the purpose of Hajj and `Umrah ; so the pilgrim either passes through the miqat itself and enters ihram from there, or he enters ihram from a place that is in line with the miqat. 
For the one who lives between the miqats and Makkah, he enters ihram from where he is. The same applies to one who comes to Jeddah and thereabouts, which is closer to Makkah than the miqats, then decides to do `Umrah: he enters ihram from where he is. 
It was narrated that Ibn 'Abbas (may Allah be pleased with him) said: The Messenger of Allah (blessings and peace of Allah be upon him) defined the miqat of the people of Madinah as Dhul-Hulayfah; that of the people of Sham (Syria) as al-Juhfah; that of the people of Najd as Qarn al-Manazil; and that of the people of Yemen as Yalamlam. And he said: “And these miqats are for the people at those very places, and besides them for those who come through those places with the intention of performing Hajj and 'Umrah; and whoever is living within these boundaries can enter ihram from the place he starts.” (Narrated by al-Bukhari (1454) and Muslim (1181). 
Passing the miqat without ihram
What your friend has to do is repent and seek forgiveness for attributing that ruling to Islam. And what you must all do – according to the majority of scholars – is offer a sheep, to be slaughtered in the Haram and its meat is to be distributed to the poor there. If any of you is not able to do that, then it is sufficient for him to repent. 
The scholars of the Standing Committee said: 
“What the one who intends to do `Umrah and then comes to the miqat must do is enter ihram from there; it is not permissible for him to pass it without entering ihram . As you did not enter ihram from the miqat, each one of you must offer a sacrifice, which means slaughtering a sheep that qualifies as an udhiyah sacrifice, to be slaughtered in Makkah al-Mukarramah and the meat distributed to the poor there; you should not eat any of it. As for not praying two rak‘ahs after putting on the ihram garments, there is no blame on you for that. (Shaykh ‘Abd al-‘Aziz ibn ‘Abdullah ibn Baz, Shaykh ‘Abd ar-Razzaq ‘Afifi, Shaykh ‘Abdullah ibn Ghadyyan, Fatawa al-Lajnah ad-Daimah li’l-Buhuth al-‘Ilmiyyah wa’l-Ifta (11/176-177) 
Shaykh Ibn ‘Uthaymin (may Allah have mercy on him) said – after a detailed academic discussion of the issue of the one who omits any obligatory part of Hajj or `Umrah: 
“In that case we say to the one who omits an essential part (of the rituals): Slaughter a fidyah (sacrifice) in Makkah and distribute its meat to the poor yourself, or appoint a trustworthy proxy among the agents. If you are not able to do that, then your repentance is sufficient and you do not have to fast. This is our view concerning this issue.” (Ash-Sharh al-Mumti‘, 7/441) 
You can also contact trustworthy organizations to offer the sacrifice on your behalf in Makkah. 
And Allah knows best.