Guidelines on the relatives with whom ties of kinship must be upheld
Question

Is the son of my paternal aunt one of the relatives with whom I must uphold ties of kinship?.
Praise be to Allah.Undoubtedly the son of your paternal aunt is one of the relatives with whom ties of kinship should be upheld and whom you should treat kindly and to whom you should be friendly. But is he one of the “rahm” relatives with whom ties of kinship must be upheld? There is a difference of opinion among the fuqaha’ concerning that. The reason for that is that relatives are of two types: mahrams and non-mahrams. The guideline on mahram relatives is: each two persons who, if one were male and the other female, it would not be permissible for them to get married, such as fathers and mothers, sisters and brothers, grandfathers and grandmothers no matter how far the line of ascent reaches, children and grandchildren no matter how far the line of descent reaches, paternal uncles and aunts, and maternal uncles and aunts. 
With regard to the children of paternal uncles and aunts and maternal uncles and aunts, they are not mahram relatives, because it is permissible to marry them. 
Non-mahram relatives are all other relatives, such as the son of your paternal aunt, the daughter of your paternal aunt, the son of your maternal aunt, the daughter of your maternal aunt, and so on. 
Some fuqaha’ are of the view that the relatives with whom ties of kinship must be upheld are the mahram relatives only. As for non-mahram relatives, it is mustahabb to uphold ties with them but it is not obligatory. This is the view of the Hanafis and is the lesser-known view of the Maalikis; it is also the view of Abu’l-Khattaab among the Hanbalis. Their evidence is that if it is obligatory to uphold ties of kinship with all relatives, it would be obligatory to uphold ties of kinship with all of the children of Adam, and that is impossible, so it is essential to set guidelines on the relationship which makes it obligatory to uphold and honour ties of kinship and makes it forbidden to cut those ties, and that is the mahram relatives. 
They also quoted as evidence the words of the Prophet (peace and blessings of Allah be upon him): “One should not be married to a woman and her paternal aunt, or a woman and her maternal aunt, at the same time.” Narrated by al-Bukhaari and Muslim (1408). Al-Haafiz Ibn Hajar said: al-Tabaraani added to the hadeeth of Ibn ‘Abbaas: “If you do that, you have severed your ties of kinship.” This was classed as saheeh by Ibn Hibbaan. And Abu Dawood narrated in al-Maraaseel a report from ‘Eesa ibn Talhah that the Messenger of Allah (peace and blessings of Allah be upon him) forbade being married to a woman and any of her relatives at the same time, for fear of severing ties of kinship. End quote from al-Diraayah fi Takhreej Ahaadeeth al-Hidaayah (2/56). 
The way in which they understood this hadeeth to prove their point was explained by some of the Maaliki scholars (may Allah have mercy on him). Al-Quraafi said: The eighth issue regarding the obligation of upholding ties of kinship: Shaykh al-Tartooshi said: one of the scholars said: rather upholding ties of kinship is obligatory if the relatives are mahrams, which refers to each two persons who, if one were male and the other female, it would not be permissible for them to get married, such as fathers and mothers, sisters and brothers, grandfathers and grandmothers no matter how far the line of ascent reaches, children and grandchildren no matter how far the line of descent reaches, paternal uncles and aunts, and maternal uncles and aunts. As for the children of these, upholding ties of kinship between them is not obligatory, because it is permissible for them to get married. The soundness of this view is indicated by the fact that it is haraam to be married to two sisters, or to a woman and her paternal aunt or to a woman and her maternal aunt at the same time, because that leads to severing the ties of kinship, and avoiding something haraam is obligatory, and honouring them and not harming them is obligatory. But is it permissible to be married to two female paternal cousins or two female maternal cousins at the same time, even if they are jealous of one another and sever ties with one another, and that is because upholding ties of kinship between them is not obligatory. End quote from al-Farooq (1/147). 
The second opinion concerning this issue is that it is obligatory to uphold ties of kinship with all of them, with no distinction between mahrams and non-mahrams. This is one view of the Hanafis and is the well known view of the Maalikis. It was also stated by Ahmad, and it is what may be understood from the general terms in which the Shaafa’is discussed this issue, because none of them singled out the mahram relatives in this regard. Al-Mawsoo’ah al-Fiqhiyyah al-Kuwaitiyyah (3/83). 
See also: Ghadha’ al-Albaab by al-Safaareeni (1/354) and Bareeqah Mahmoudiyyah (4/153). 
There are other opinions concerning this matter. It says in Subul al-Salaam (2/628): It should be noted that the scholars differed concerning the definition of the relatives with whom it is obligatory to uphold ties of kinship. It was said that it is relatives with whom marriage is haraam, such that if one of them were male marriage to the other would be forbidden. Based on that, it does not include the children of paternal or maternal uncles and aunts. Those who hold this view quote as evidence the fact that it is haraam to be married to a woman and her paternal aunt or maternal aunt at the same time, because that leads to severing of ties of kinship. 
And it was said that it is those who are connected by inheritance which is indicated by the words of the Prophet (peace and blessings of Allah be upon him), “then the next closest and the next closest.”  
And it was said that it refers to those who are related to one another regardless of whether they are connected by inheritance or not. 
Moreover, upholding of ties of kinship, as al-Qaadi ‘Iyaad said, is of varying degrees, some of which are higher than others. At the very least, it is not forsaking one another, and upholding ties by speaking, even if it only saying salaam. That varies according to possibility and need. It may be obligatory or mustahabb. If a person upholds ties to some extent, even if it is not to the fullest extent, he cannot be called a breaker of ties of kinship, and if he fails to do what he is able to do and should do, then he cannot be called an upholder of ties of kinship. 
Al-Qurtubi said: The degrees of relationship which must be upheld are general and specific. The general relationship is that which is based on religion, which must be upheld by means of mutual love, sincerity, fairness and fulfilment of rights both obligatory and mustahabb. 
In addition to that, the specific relationship also involves spending on relatives, checking on them and overlooking their mistakes. End quote. 
This is a summary of what the scholars have said about this issue, but what has been narrated about the great reward for upholding ties of kinship and the severe punishment for severing them will be no secret to you. This means that you should be keen to uphold ties of kinship and beware of severing them, and be on the safe side with regard to your religious commitment, and avoid an area concerning which the scholars differed. So hasten to uphold ties of kinship with the son of your paternal aunt, and treat him kindly as much as you can, for the reward of that will not be lost with Allah. 
See also the answers to questions no. 12292, 22706 and 4631. 
May Allah help us and you to do that which He loves and which pleases Him. 
And Allah knows best.