If you're processing the payments using Payments Pro (PayFlow or DoDirectPayment) then each seller would need Pro enabled on their own account, and you'd need to have them setup Permissions or use the Permissions API to make API calls on their behalf.
If you go with Express Checkout you can just set the PAYMENTREQUEST_n_SELLERPAYPALACCOUNTID parameter to the email address of the PayPal account you'd like the money to fall to. That will work without any permissions necessary.
Note: the n in the parameter name would be a 0,1,2,etc. depending on how many payments were included on the order. With a single payment you would just use PAYMENTREQUEST_0_SELLERPAYPALACCOUNTID=some@emailaddress.com