You are clearly academically qualified to attend either Harvard or Stanford (or one for undergrad and the other for grad school). Unfortunately, so are at least 80% of the other applicants.
In terms of your ECs, it looks to me as if you have done what was right for you, and done it very well. This is exactly the approach that I would recommend, and is also my understanding of the approach recommended in the “applying sideways” blog on the MIT admissions web site (which is also a good approach for other top schools such as Harvard and Stanford).
I would put your chances as being similar to the overall acceptance rate, or perhaps a little bit better than the overall acceptance rate. I think that both are definitely worth an application, but that both are reaches for you and for nearly everyone else.
I agree with this. I think that you are going to do very well wherever you end up.