Not clear what are you asking for, are you looking for a sort of referal program?
You can decide which paypal account will receive the money both with REST and Classic API. For example using ExpressCheckout you can specify the seller account that will receive the money.
without IPN you will miss all the stuff happening to the transaction, ie:
- payment with a different currency can result in a pending state (money conversion)
- dispute
- etc
A multiple receiver scenario could be implemented with adaptive payments: https://developer.paypal.com/docs/classic/adaptive-payments/integration-guide/APIntro/
- "Parallel payments enable a sender to send a single payment to multiple receivers"
- "Chained payments enable a sender to send a single payment to a primary receiver. The primary receiver keeps part of the payment and pays secondary receivers the remainder."