SCEA still allows you to apply to public and foreign universities. UK universities are both.
You can’t do both art and law. Choose one or the other and demonstrate that’s all you are focused on (i.e. relevant ECs, summer internships/courses etc). If law you’d better have a good answer for why studying law in the UK makes sense for your career plans (e.g. are you are dual national who wants to work in the UK?). Art history will be a very small number of students almost anywhere.
Your qualifications are in the ballpark. For Oxbridge there is usually a pre-test and always an interview, which is essentially a really tough oral exam on your subject.