Merchant Security Updates: Learn how security upgrades may affect your integration at the 2016-2017 Merchant Security Roadmap Microsite
Payments Standard Updates: Beginning March 29th 2017, PayPal will offer a few enhancements that may require integration changes. Read more here: Payments Standard Upgrade FAQ
But your correct on the fees, there would be a fee for receiving the payments and a fee for the PayOut to the next party.
I also don't see a way to for a customer to use their own paypal username and password via the api. I believe this must be to prevent any develop using the api to actually touch a paypal user account. Do you see any way to use the api to send or receive payments using a paypal user account?
Can you contact me?
sssaltman at pmfbeta.com. We are a US company doing the same thing and discovering the same issues.
I contacted you quite a while ago, but did not get a reply. Maybe my mail is stuck in your spam folder?
We are in the same boat as you. I'm curious to know how you solved it. Is there a way to get in touch?