No, I don't think you have a good shot at getting in. But that has zero reflection on your application! All of these schools have sub-10% acceptance rates, all of which are lower for international students and much lower at UChicago and Brown if you are applying for need-based financial aid. NO ONE has a good shot at getting in. So if you want someone to tell you that they think you'll get in, unfortunately, no one can do that, simply based on their acceptance rates.
But definitely apply! That's all we can encourage you to do. I don't think you'd be completely wasting your time applying.
I will be honest, your GCSEs are definitely on the low side for these schools and your extracurriculars are on the light side (try and find/develop your existing ECs to have that one EC that is memorable and really stands out if you can - develop your spike). But of course, these schools also look at your predicted A-level grades which look like they'll be great, letters of recommendation, and your essays to determine whether you would be an academic and social fit for their school. And those are not things that people on TSR can determine. All you can do is apply, hope for the best, but also prepare for the worst by having backups, either in the US or in your home country.
One thing: definitely consider doing ED at Brown or UChicago as it will give you a slight application boost. SInce UChicago has EDII, you could ED at Brown and if you don't get in, EDII at UChicago. Definitely give it some good thought.