What is the ruling of Sharia regarding the dispute between a father and his maternal uncle concerning the repayment of a debt whose value is a fluctuating currency, and what is the correct Sharia stance on the family boycott resulting from this dispute?

It is obligatory for your maternal uncle to repay the loan to your father if he is able. Your father is not permitted to demand an increase on the loan amount due to a change in currency value.

Islamic law commands upholding kinship ties and forbids severing them or harboring animosity. Therefore, your mother should be dutiful to her mother and maintain ties with her siblings, even if they are unjust. It is not permissible for her to prevent you from maintaining ties with your relatives. You are not obliged to obey your mother if she forbids you from upholding kinship ties. You can maintain these ties without her knowledge, such as through phone calls or similar means. Strive to gently advise your mother to be dutiful to her mother and to uphold ties with her relatives. Strive to reconcile them, as there is a great reward in it, for reconciliation is superior to the status of fasting, prayer, and charity.