Oxbridge, LSE, UCL and Edinburgh as a french high school student int the United States. Please help!

You might want to also consider McGill in Canada. I think as French citizen you would only pay the local rate.
What did you study any other foreign language besides French and English? Competitive schools might look at that.

Two closely related courses (such as the 2 you name) would be fine.

Be aware that (anecdotally) LSE can be harder than expected for people applying with US credentials.

The down side is that if you aren’t Accepted for one course, it would seem unlikely that you would be accepted for one so similar at The same university, so it would be a waste of a slot On your UCAS form.

Yes I am also very interested in McGill, however I am not learning any other languages. And I understand that the LSE would be hard to get into, so any advice on which universities I should be aiming for if I want to study finance based on my stats?

Schools I am looking at so far are the LSE, KCL, Edinburgh, UCL, Imperial College, Oxford, St Andrews.

Imperial only offers science subjects so what would you study there?
Of the others, Oxford and LSE would be very tough admits, UCL nearly as hard, then KCL, Edinburgh and St Andrews all look like reasonable possibilities. But its not at all certain that you’d get an unconditional offer with only 3 APs to date. Have you considered doing some SAT IIs so you have those scores in hand when you apply?

You mean that my Physics (780), Math II (800) and less importantly French (800) subject tests will not count as much as they should if I choose to go into finance?

Well your French won’t count twice and as a native speaker may be somewhat (perhaps totally) discounted. Your math and physics SAT 2s are helpful but I was thinking more about how you could fill in some breadth beyond Comp Sci/Stats/Math/Physics which is a very narrow focus, especially for someone who is not applying for math. It will likely hurt your prospects of receiving an offer at some of the top schools on your list, especially with a sub-1500 SAT. Remember that UK students demonstrate breadth via their 8-10+ GCSEs and are expected to get almost all As/A*s in them for top schools.

For example LSE says (http://www.lse.ac.uk/study-at-lse/international-students/country-pages/united-states-of-america):
“Applicants should also bear in mind our general preference for a broad mix of traditional academic subjects to be offered.
AP Language and Culture courses may be excluded where students have significant prior exposure to that language.”

That about the French schools? Especially considering when it comes financial engineering France is famous for its quants. You can always return to the US for graduate school afterwards.

If you’re very into math and physics you could try the Polytechnique Bachelor’s.

Yes that’s actually my top choice, but do you know what kind of stats are needed to get to get admitted?