Is it permissible for my son to give money to his paternal uncle with the intention of helping him, fearing a قطعيه (severance of ties), and out of gratitude, and is it permissible for the uncle to take it?

There is no harm for a debtor to pay his creditor more than his debt, as a gesture of good repayment, if it is not based on a promise or an agreement. Otherwise, it would be usury. In the aforementioned issue, the increase is not permissible because it is based on a promise from the husband. Deception does not change the ruling in any way. Therefore, the increase is forbidden usury according to the Qur’an and Sunnah. The Prophet cursed the one who consumes usury, the one who gives it, the one who records it, and its two witnesses. Deceiving to engage in usury increases the sin, as happened with the Jews, who were cursed when they resorted to deception concerning God’s prohibitions.