Yes, you may submit 2 receipts of >$20 each in the same transaction (one after the other).
I haven't received mine yet so I don't know what they will mail ($10 coupon or 2 X $5 coupon).
My guess would be 2 X $5 coupon in one envelop.
The instructions are clear and easy to follow.
Put all the chances on your side for an easy experience: make 2 pdf: one for each receipt.
Or 2 jpeg: one for each picture of each receipt (separate).
If it's not obvious, highlight, underscore or encircle the merchant's name, the date, quantity and description of the products.