Open APIs

Hi All,

I have two use-cases for account relationships to be managed within Billing Account Management and want to understand the right option 

1. Consolidated Billing : Want to set up relationship between multiple/group of billing accounts to map to one BIlling account so all charges from the group of Billing accounts can be billed together under a parent billingaccount based on its bill structure.
   1. Can I map this relationship of many to 1 using BillingAccounts -> AccountRelationship -> AccountRef -> BillingAccount (parent) or 
   2. Can I extend BillingAccount resource to include parentId and manage relationship directly between billingaccounts to maintain parent - child relationship
2. Associate billing account from an external billing system to a BIllingAccount within our billing system just for reporting purposes
   1. Should I again use AccountRelationship with a different relationshipType to define the type of relationship between 2 accounts?

Thanks

Can someone suggest any way forward in terms of the relationship between accounts? Thanks.