Escrow Deposits And Vat Registered / Not Registered

Suppose we are using MV PayPal for Marketplaces. Client is transferring money to site owner, then the latter is releasing money to vendor. How is that problem solved accounting-wise for the following cases?

1. Vendor and client are VAT-registered, site owner is not.

2. Vendor is NOT, site owner is VAT-registered.

3. Client is EU VAT-registered or non-EU customer, vendor is NOT REGISTERED, site owner IS. Both vendor and site owner are in the same EU country.

4. Same as 3, but vendor and site owner reside in different EU countries.


Then here comes the problem with declaring VAT...