Are the Sofia suede sandals waterproof?

They are suede, not waterproof, but they are super comfy, live mine!!

Color granite -- is it grey or beige or greige?

That's a tough one, but I like your name of "greige". It would definitely lean more to the grey side, but not so much that you couldn't wear it with beige. I really think could go either way. Maybe kind of a putty color, more on the warm side of "greige" than cool.

If i return will the shipping cost will also be refunded? Also do i need to pay for return shipping?

As a Prime member the initial shipping was free as was the return shipping so I do not know about refunding of shipping cost or payment for return shipping if not a Prime member.

I have a high instep will the strap fit you think?

The strap doesn’t go across your instep. Higher up towards the ankle. The bottom portion around toes doesn’t come up to the instep. Probably a good choice for you.