Khalwah if Another Woman is Present

Firstly: 

The scholars (may Allah have mercy on them) are unanimously agreed that it is haram (impermissible) to be alone with a non-mahram (a woman whom one is allowed to marry according to Islamic law) woman (khalwah), because of the saheeh hadeeth (authentic narration): “No man should be alone with a woman unless there is a mahram (male relative whom she could never marry) with her.” Narrated by al-Bukhari, 5233; Muslim, 1341. 

An-Nawawi (may Allah have mercy on him) said: If a non-mahram man is alone with a non-mahram woman, with no third person present, this is haraam according to scholarly consensus.

End quote from Sharh Saheeh Muslim, 9/109 

As-San‘ani (may Allah have mercy on him) said: This hadeeth indicates that it is haram to be alone with a non-mahram woman, and there is consensus on this point.

End quote from Subul as-Salam. 1/608 

Secondly: 

There is nothing wrong with a woman allowing a non-mahram man to enter her husband’s house when he is absent, as long as two conditions are met:

1.     Her husband should have given her permission to do so.

2.     There should be no khalwah (i.e., she should not be alone with him); rather there should be a mahram with her such as her father or brother, or anyone for whom it is permanently forbidden to marry her. 

If she does not have a mahram with her, but there is another woman with her, khalwah may be avoided thereby, but it is not permissible for a woman to put herself in such a situation unless the woman is trustworthy and the man who is with them in that place is also trustworthy and there is no fear that he could overpower the two women. 

An-Nawawi (may Allah have mercy on him) said: If a non-mahram man is alone with a non-mahram woman, without a third person being present with them, this is haram according to scholarly consensus; this is different from if a man is with a number of non-mahram women, in which case the correct view is that it is permissible.

End quote from Sharh Saheeh Muslim, 9/109 

As-San‘ani (may Allah have mercy on him) said: It says in the hadeeth that “the third one present with them is the Shaytan”. Can someone other than the mahram take his place in that regard, so that there will be someone with them in order that khalwah will be avoided? It seems to be the case that he may take his place, because the reason for the prohibition is the fear that the Shaytan may cause temptation between them.

End quote from Subul as-Salam, 1/608 

Based on this, there is nothing wrong with the man allowing a non-mahram to enter his house, on condition that he is not alone with his wife and that he is trustworthy. However, the basic principle, and the best precaution to safeguard religious commitment, is that he should not allow this unless there is a mahram present. 

And Allah knows best.