I want to build a shopping cart , but can't find a solution to integrate bitcoin and ethereum without a third party

Steps i want to do :

1.User adds to cart
2.User writes in form shipping info etc
3.I want to show my btc and eth addr so user can pay for product
4.After user makes payment  and 3 confirms redirect user to shopping cart and send order email

Can't figure it out how to do it without a third party ... an ideas ?