Is the questioner sinful for not attending his father’s funeral because his siblings rushed the burial? And is he sinful for his father spending the money he used to send on his siblings? And is he sinful for refusing his father’s request to live in the city? And is it permissible to pay off his father’s debt from the remaining zakat money?

You are not sinful for not attending your father's burial. What your brothers did by expediting his burial is preferable, in accordance with the Sunnah (definition).

You can benefit your father after his death by supplicating for him, seeking forgiveness for him, and giving charity on his behalf. Every act of worship you perform and dedicate its reward to him will benefit him, Allah willing.

You were not sinful if you were providing your father with the obligatory maintenance, and he then gave it to his children. As for your spending on him during his illness and your spending on your siblings, and his supplication for you, we hope you will receive the reward for that.

As for the amount designated for zakat (definition), it was not permissible for you to give it to your father if he was wealthy, even by means of his obligatory maintenance. You are responsible for this money and must give it to its rightful recipient. However, if you were unable to afford your father's medical treatment, there is no harm in taking it from zakat funds. It is not permissible to pay the debt of the deceased from zakat.

You must spend the remaining amount on its designated purpose, or return it to the one who entrusted it to you.