Transfer between two customers (Peters Rental account to Peters Private account)

Transfer between two customers (Peters Rental account to Peters Private account)

we are a Property Management company.
Our customers have to accounts (registered as two customers - Peter Rental and Peter Private
On the rental account all income and costs fron rental activities are noted.
On the private account all private are noted
to pay the private invoice we need to transfer "money" from the rental account to the private account and pay the private invoice.
we have made an invoice earlier but this option may not be available now when Spain starts to use Verifactu.
have you any solution 
peter