Are the brother-in-law (husband of the sister), the husband of the paternal female cousin, the paternal uncle of the paternal male cousin's son, and the paternal grandfather's brother considered to be among the kinfolk whose ties must be maintained, and does sin befall one who falls short in maintaining ties with them?

Scholars have differed on defining the kinship ties (Arham) that must be maintained:

The First Opinion: This pertains specifically to mahram (unmarriageable kin) relatives. This is the view of some Hanafis, Malikis, and Hanbalis. They argued that obligating the maintenance of ties with all relatives is impossible, hence the obligation of maintaining ties was restricted to mahram relatives. An example of this is the prohibition of marrying a woman concurrently with her paternal or maternal aunt, as it severs kinship ties.

The Second Opinion: This includes every relative, whether mahram or non-mahram. This is the view of the Hanafis, and the well-known opinion among the Malikis, Ahmad, and the Shafi'is. They cited the hadith, "Then the closest, then the next closest," and the Prophet's maintenance of ties with the people of Egypt due to their kinship, and the hadith: "Indeed, the most virtuous righteousness is for a son to maintain ties with the loved ones of his father."

The more preponderant view is that the kinship ties that are obligatory to maintain are those with every mahram relative, while maintaining ties with other relatives is commendable (mustahabb).

The paternal uncle and the grandfather's brother are among the kinship ties that are obligatory to maintain.

Whereas the sister's husband and the paternal cousin's daughter's husband are not among the Arham but rather in-laws (as-haar), so maintaining ties with them is not obligatory.

Maintaining kinship ties involves being good to them according to the circumstances of the one maintaining the ties and the one with whom ties are being maintained, whether through money, service, visits, greetings, and so forth. This is subject to custom. Visiting relatives is not obligatory unless custom considers neglecting it to be an act of severance.