Harvard, Yale, Stanford ,Columbia university

Hi
Im an international applicant.
If I convert my Gpa to american system itll be around 3.4 and in my own country it is 17/20 and concidered A- … [18 to 20 is A+] [16 to 17.99 is A-]
But the problem is Ive got th total of 2 or 3 of 12/20s on finals from freshman year to senior year. My highschool is a charter School ( It is called School for Exceptional Talents).and is so competetive and selective w acceptence rate of 1 percent and we take harder tests than other highschoolers so the grades are not expected to be +As here.
Im not pretty sure how Im goin to explain it to colleges haha
I have some high ECs.
High ACT score of 36.
SAT subjects tests in Math L2 800 , Bio/m 800 Phys 800 but im planning to take Math L1 and bio/E and Chem in October and Im expecting 3 other 800s(hoping that theyll offset my low GPA)
Do I have any chances to Harvard Stanford Yale or Columbia? or am I going to be rejected as to my gpa?
to which one should I apply REA?
Harvard early action deadline is on November 1st … will it be ok if I take the Subject tests on November 3rd? Ive heard it is ok so im just asking to make sure