Is it permissible to stop or reduce the monthly financial amount that a son sends to his father, especially after the father married a girl much younger than him, and the children gave up their mother's jewelry to help with the marriage, knowing that the father has a large pension and has deluded the bride's family with his wealth?

The father's right is great, especially in old age. It is obligatory to honor him, obey him, and not forget his favor. Spending on a poor, needy father is obligatory by the consensus of scholars. If he is not needy, then spending on him is not obligatory, but it is obligatory to maintain ties with him and treat him kindly. Helping the father with marriage and spending on his new wife is a righteous deed and does not contradict the love for the deceased mother.