There is a fairly robust PayPal Developer community with online resources. If you do not immediately understand their manuals, some of which are pretty opaque, you might want to engage one of the experienced developers to write the code you need.
Best online docs I have seen for Mass Pay:
https://cms.paypal.com/us/cgi-bin/?cmd=_render-content&content_ID=developer/howto_api_masspayAccess to the Developer Network (registration required):
https://www.paypal-portal.com/community/HTH, ~Ray