What is the Sharia ruling on my refusal to pay the amount my father is demanding, claiming it is the cost of my dowry and educational expenses, especially since he did not ask my siblings for this, and I am married with a child, studying abroad, and paying it would cause significant financial and psychological harm?

A father must marry off his poor and needy children, but this does not apply to you because you are capable of earning. It is permissible for a father to take money from his son if he needs it and it does not harm the son, or to take it to give to another brother, for "you and your wealth belong to your father." You should reassure your father and explain to him that you do not currently have the full amount, and give him what you can without harming yourself or your dependents, especially since he wants the money for your needy brother, and this is a form of filial piety. A father's supplication (dua) against you without just cause will not harm you. Appease him with kind words and giving. Thank Allah for His blessings of knowledge and sustenance through your dutifulness to your parents and maintaining ties with your siblings. Do not let worldly matters cause the severance of kinship ties or disobedience to parents. It is a sign of noble character and gratitude to give your father money even if you are in need of it, and Allah will compensate you.