Hello,
Not very easy. It would be easier to say a min of $20 for the 2 items by setting "Minimum order total" to 20 specific in the "Min Qty 2" coupon.
Can't think of a way to do what you want through the coupon code, the only thing I can think of is to create a category for 10 and up products, add all products that belong to that category and then include the category in the coupon. Or the other way around, all products that dont belong to 10 and up and exclude the category in the coupon.