Split the customer payment to vendor and to owner

I'd like to use hikamarket and hikashop to realize this kind of e-commerce service:

1) customer
2) vendor
3) marketplace owner

In my marketplace you can find a lot of different vendor that put in sale their products.
I'm the owner of the market place and i take a 20% of the product price from the vendor and i produce an invoice for this service
The vendor will produce an invoice of the 100% of product's price to the customer.

The customer will'pay using paypal or other service.

The payment arrive to vendor or to marketplace owner?

I need the money that start from the customer split in this way:
1)80% to the vendor
2)20% to the marketplace owner

In this way I can produce the invoice for the vendor for the service my marketplace offer (20% of commission)

Is it possible? How can i do?

I must provide an invoice for just the 20% of what I earned from the vendor and also I must provide an invoice to the vendor and not to the customer. The vendor must provide and invoice to his customer about the 100% of the payment (+tax, etc...) and I just have to generate an invoice for the vendor about the 20% (+tax, etc...)
About the payment process I understand how it works now. That means that I receive money for something that I do not sell! Then I send those money to someone else... that's not really good...
Why not just disable with an option the ability for the customer to buy many goods and just buy one good at a time? This way you could let customer pay directly the vendor and with PayPal adaptive plugin vendor pay me automatically my 20%. This way I just manage money for the services I provide, and I do not manage money for something that I didn't sold! That can be very risky in fiscal controls!
In most cases people buy just one thing over the e-commerce. Would you consider this?