Assalamualaikum...
I love my cousin so much and wanted to marry him. But my mother is not ready for our marriage.
Though his parents are supporting our marriage.
I don't have a father not even a brother, but i have 3 uncles(brothers of my father) and they are also opposing my decision.
They want me to get married to a boy of their choice without my consent (forcefully).
They are not even ready to listen to me.
And i wanted to is it permissible for me to perform a court marriage without consent of my mother and my uncle's(my legal wali) or should i marry a guy of their choice under their pressure?

All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.

Neither your mother nor your paternal uncles have the right to force you to get married to a person you dislike. However, if this man they want you to get married to is a religiously-committed person whose qualities might help establish a continuous martial bond, then accept marriage from him in fulfillment of your dutifulness to your mother and paternal uncles, and this dutifulness might be a reason for blessings in this marriage.

Yet, if you insist on your opinion not to get married to this person and want to marry your cousin instead, then try to convince your mother and paternal uncles. In doing so, you should seek the help of those people who might positively change their opinions. And first of all, you should seek the help of Allah, the Exalted, through making supplications to Him. So, if they get convinced – thanks to Allah – then you have achieved your goal; otherwise, you should report your case to the authority specialized in examining Muslim issues to convince them to allow you to get married to the person you want or to let the judge or whoever represents him do so.

Allah knows best.