Hello.
If you just resubmit it and edit some stuff, then yes that will likely qualify as plagiarism.
At A level, especially for coursework, you are expected to do the work yourself. Therefore you can take ideas from your brothers work and put them into your own words (paraphrase, including citing and referencing), but you need to really do your NEA yourself based from your own or similar research. Moreover, because his NEA was A* quality you may find that the teachers marking it may well recognise it as it was only three years ago he submitted it. I really wouldn't risk it, as if they catch you, you may get a 0 for your NEA and you could potentially be barred from taking examinations in this course for a set period of time. That's if your department report it to the exam board and they choose to be draconian (that's post singing a declaration saying it was your work, I think).
Please be careful with the academic quality of your work. If the work is due next academic year, you have time to do it. Do not worry so much about it. You can use your brother's work as reference material and a spring board for ideas, but don't just resubmit it 🙂