Is it permissible to disobey one's father and use his computer to seek religious knowledge and acquire religious books, and what is the ruling on using the books that have already been acquired or have not yet arrived, and is it obligatory to cancel their order?

As long as the computer belongs to your father, it is not permissible for you to use it, even for seeking religious knowledge or purchasing religious books, except with his permission. The owner of a possession has a greater right to it, and it is not permissible for anyone to dispose of it without his permission, due to Allah's saying: "O you who have believed, do not consume one another's property unjustly," and due to the Prophet's (peace be upon him) saying: "The property of a Muslim person is not lawful except with his willing consent."

Instead of acting without his permission, discuss it with him and try to convince him to allow you, or seek intercession from those who have standing with him. As for the books you have acquired, there is no blame upon you for benefiting from them, while refraining in the future from using the computer except with your father's permission.