Five years ago I said to my wife that if any of your sisters or their sons enter to my house you will be divorced, I meant it since it was after they harmed me a lot. Things changed since then and they are in a very bad situation and two days ago one of their sister's son came to my house and I did not let him enter but my wife told my son to let him in and I did not object. Will my wife be divorced from me now, considering the fact that I did not object to his entering my house?

Praise be to Allah, the Lord of the Worlds; and blessings and peace be
upon our Prophet Muhammad and upon all his Family and Companions.
The mentioned situation in your question depends on your intention and what you meant when you made the divorce dependent upon a sister of your wife or her sons entering your home.
If there was a particular reason, which led you to make the condition and that reason no longer exists, then there is no harm whether the son or your sister in-law entered with your knowledge or without it. Just as there is no harm for any person to enter your house whom you had once objected to enter if the reason no longer exists. But if the reason still exists, or you objected to those particular relatives without any reason then the condition for divorce has been met.
In this case Muslim scholars have different opinions.
The majority of the Muslim scholars are of the opinion that the conditional divorce would be effective when the condition occurs.
Some other Muslim scholars are of the opinion that divorce depends on the intention of husband:If he intends conditional divorce whenever the condition is met, the divorce would be considered legally effective and valid. If he intends only to urge her to do something or to deter her from something and does not intend a conditional divorce, it would not be considered a divorce. Rather it is considered an oath, thus he has to pay the expiation of breaking an oath. We advise you to follow the saying of the majority of the Muslim scholars for the following reasons.
1. Most probably a man intends a divorce rather than to urge something or to make an oath. When he intends divorce all scholars agree that it is
considered a valid divorce.
2. Implementing the first opinion is safer and further from any kind of
doubt.
3. If this is the first divorce or second divorce then the solution is very
easy. First and second divorces are revocable divorces. So you may bring her back to conjugal life without any condition if she is still in her
waiting period since that son entered your house. The waiting period starts from the time of divorce. Bringing her back to conjugal life during her waiting period does not need Mahar nor renewing the marriage contract nor permission of the wife or that of her guardian, etc.
If the waiting period has ended then in order to take her back you need to have a new marriage contract, fulfilling all the conditions of a valid
marriage, such as the consent of wife and her guardian, paying Mahar, etc.
Furthermore, we remind you that what you did is a major error; hence you are in a dilemma and do not know how to resolve it.
It was very possible for you to prevent your unwanted relatives from
entering your house without endangering your marriage. Even preventing them from visiting your wife is tolerable if their visit causes any actual religious problem or other harm. If there is no such harm then you have no right to stop them from visiting since it strengthens kinship relations, which is promoted by Islam.
Allah knows best.