Firstly: 

May Allaah reward you with good for your eagerness to cover and remain chaste, and to make precautions, and to advise and guide the teachers and students. This comes under the heading of fulfilling the trust. 

Secondly: 

We cannot say that it is obligatory for a Muslim woman to cover the face with a multi-layered khimar. What is required is for her to cover the face, whether it is with a single layer or several layers. 

Islam allows the khimaar and the niqaab. Those scholars who disallow the niqaab do not do so because it is not prescribed in principle, rather it is because some women choose a type of niqaab that does not meet the  shar’i conditions, such as making the opening for the eyes too big. The same may also be said of the khimaar. It is not disallowed in and of itself, but because of its nature, if the fabric is too thin and the face can be seen through it.  

The scholars of the Standing Committee were asked about the Islamic ruling on the niqaab. They replied:  

As for the niqaab, Abu ‘Ubayd said, concerning the definition of niqaab among the Arabs: It is that from which the socket of the eye appears, and they used to call it al-waswasah or al-burqa’. As for the ruling concerning it: it is permissible. It was originally mentioned in the report narrated by ‘Abd-Allaah ibn ‘Umar (may Allaah be pleased with him) who said: “A woman in ihraam should not wear niqaab or gloves.” According to another report he said: I heard the Prophet (peace and blessings of Allaah be upon him) forbid women to wear gloves when in ihraam. 

The fact that the Prophet (peace and blessings of Allaah be upon him) forbade the woman in ihraam to wear niqaab indicates that it is permissible to wear it when not in ihraam. Moreover it cannot be understood from this hadeeth that it is permissible for the woman in ihraam to uncover her face if non-mahram men can see her; rather she must lower the khimaar or niqaab (over her face) until they have passed her. The basic principle concerning that is the report narrated by Imam Ahmad, Abu Dawood and Ibn Majaah from ‘Aa’ishah (may Allaah be pleased with her) who said: The riders would pass by when we were with the Messenger of Allaah (peace and blessings of Allaah be upon him) in ihraam. When they drew near to us one of us would lower her jilbab from her head over her face, and when they had passed by we would uncover (our faces). End quote. 

Shaykh ‘Abd al-‘Azeez ibn Baaz, Shaykh ‘Abd al-Razzaaq ‘Afeefi, Shaykh ‘Abd-Allaah ibn Ghadyaan, Shaykh ‘Abd-Allaah ibn Qa’ood. 

Fataawa al-Lajnah al-Daa’imah (17/171, 172). 

Shaykh Muhammad ibn Saalih al-‘Uthaymeen (may Allaah have mercy on him) was asked: 

What is the ruling on the burqa’ (niqaab) if it is not worn for adornment, but for covering, and also wearing a cover (on top of it). 

He replied: 

There is nothing wrong with it, because it will not be seen, as it is going to be covered with something over it. But as for the burqa’ that is on the face and is not covered, we do not say that it is permissible, because it is fitnah and because women do not limit themselves to that. If women would stick to the eye opening then we would say that this is niqaab, which was known at the time of the Messenger (peace and blessings of Allaah be upon him) and there is nothing wrong with it. But believe me, if you say that it is permissible for women to wear niqab up to the eyes and look out from behind the niqab, within a short time the hole in this niqab would widen to include the forehead and cheeks, then the cover would decrease until the whole face is exposed. This is well known to be the way of women, so shutting the door to that is the best way. End quote. 

Liqa’aat al-Baab il-Maftooh (14/question 43) 

Based on that: 

We say to the teachers, sisters and all Muslim women: whoever among you wants to cover her face has chosen that which is most concealing for herself, and that which is better for religious commitment. But she has to adhere to the prescribed shar’i form of khimaar or niqaab. It is not permissible to make the opening of the niqab to show more than the eyes, and it is not permissible to make the khimaar so thin that it shows the face. 

It was narrated from ‘Alqamah ibn Abi ‘Alqamah that his mother said: Hafsah bint ‘Abd al-Rahmaan entered upon ‘Aa’ishah the Mother of the Believers, and Hafsah was wearing a thin khimaar. ‘Aa’ishah tore it and gave her a thick khimaar to wear. 

Narrated by Maalik in al-Muwatta’ (1693) and al-Bayhaqi in al-Sunan (2/235). Its isnaad is hasan.  

Ibn ‘Abd al-Barr said: 

Any garment that shows the shape and does not conceal, it is not permissible to wear it under any circumstances, except with another garment that does conceal and does not show the shape, for the one who wears it is in effect naked, as Abu Hurayrah said, and this is narrated from the Prophet (peace and blessings of Allaah be upon him) in the hadeeth of Abu Hurayrah. End quote. 

Al-Istidhkaar (8/307). 

One other thing: Your responsibility in the Qur’aan memorization centre is to make the teachers and students observe the covering that is required of them inside the centre. As for what happens after they leave the centre, or before they get there, is not your responsibility, but you should advise them and teach them, without forcing them to wear something in particular. 

We ask Allaah to guide you to all that is good, and to guide the teachers and students to that which is good and proper. 

And Allaah knows best.