Marketpress Commerce and PayPal IPN

Hi, I'm building a Multisite Website for me and my close friends.

Inside the site we intend to put Marketpress Commerce, so each and everyone of us can build a store. However, a problem arose regarding Paypal and we need to know if it's possible to overcome it.

1. if a person creates multiple sites in this MultiSite, can he use the same IPN to sell his products?
2. each person will have it's own IPN code. Is possible to use different IPN codes on different sites? Or is the IPN code global for the entire network of sites?

Thanks
Enrico