Status of Maternal Aunt in Islam
Question

What should be the relation between a nephew and his maternal aunt? Can he shake hands with his maternal aunt? What is the status of the maternal aunt in Islam? What are her rights? Can she expose her face in front of her nephew? Please explain in detail.
Praise be to Allah.Status of maternal aunt in Islam
The maternal aunt has a high status in Islam, which is similar to that of the mother. Abu Dawud (2278) narrated from ‘Ali (may Allah be pleased with him), from the Messenger of Allah (blessings and peace of Allah be upon him), that he said: “The maternal aunt is of the same status as the mother.” (Classed as sahih by al-Albani in Sahih Abi Dawud) 
It was said that what is meant is that she is of the same status as the mother with regard to being entitled to custody, because the hadith was narrated concerning that. (Fath al-Bari, 7 /506) 
It was also said that her status is equivalent to that of the mother with regard to custody and other matters. 
Adh-Dhahabi said in al-Kabair: “That is, with regard to showing kindness, honouring, and upholding ties of kinship with her.” (Sharh Bulugh al-Maram by Shaykh Ibn ‘Uthaymin, 5/203) 
Rights of maternal aunt in Islam
The second meaning is supported by the report narrated by at-Tirmidhi (1904) from Ibn ‘Umar, according to which a man came to the Prophet (blessings and peace of Allah be upon him) and said: O Messenger of Allah, I have committed a grave sin; can I repent? He said: “Do you have a mother?” He said: No. He said: “Do you have a maternal aunt?” He said: Yes. He said: “Then treat her kindly.” (Classed as sahih by al-Albani in Sahih at-Targhib, 2504)  
This indicates that honouring one’s maternal aunt and treating her kindly come under the heading of virtuous deeds and acts that expiate sins. 
Abu Dawud (4970) narrated from ‘Aishah (may Allah be pleased with her) that she said: O Messenger of Allah, all my friends have a kunyah. He said: “Call yourself by the name of your son ‘Abdullah” – meaning the son of her sister. Musaddad said: ‘Abdullah ibn al-Zubayr. He said: So she was known by the kunyah of Umm ‘Abdullah. He was ‘Abdullah ibn az-Zubayr, the son of her sister Asma (may Allah be pleased with them all). 
This hadith confirms what is mentioned above, that the maternal aunt is of the same status as the mother. 
So the Muslim should treat his maternal aunt in a kind manner, just as he treats his mother. 
Is your maternal aunt the maternal aunt of your descendants?
A person’s maternal aunt – or his paternal aunt – is a maternal aunt to him and to all of his descendants, or a paternal aunt to him and all of his descendants. So your father’s paternal aunt is a paternal aunt to you, and your father’s maternal aunt is a maternal aunt to you; the same applies to your mother’s paternal aunt and maternal aunt. 
Is your maternal aunt a mahram?
A man’s maternal aunt is one of his mahrams , so it is permissible for him to shake hands with her, be alone with her and travel with her, and it is permissible for her to uncover her face in front of him, as a mother does in front of her sons. 
It is permissible for a Muslim woman to uncover in front of her mahrams and women like her that which usually is the case with people of religious commitment and good conduct, such as the face, head, neck, forearms and part of the shin. 
It is not permissible for her to wear short or see-through clothes in front of them, or tight clothes that show the shape of the ‘awrah . 
And Allah knows best.