This question already has an answer here:
I am a 25-year old Muslim woman living in the UK with my parents and siblings, and I have been in love with a non-Muslim man for 3 years. We agree this will not lead anywhere, both out families would not agree.
We thought about him converting, so I asked my mum if I can get married to a convert, but she said no. I don’t want to go against my parents decision, plus the Nikah wouldn't be valid without my parents' consent.
I explained the situation to my brother, that I don’t want to get married to anyone else. He said if he converts, I have permission to marry him.
If I go ahead with this Nikah when my parents do not agree and my older brother gives me his permission, will the Nikah be valid? I have 2 older brothers that will be there with me.
I asked the first part of my question here: Can a girl tell her parents that she doesn’t want to get married at all?