Rollup By Lookup (RBL) is a feature in Financial Services Cloud that allows you to display summary calculations of financial account information, such as balances, market values, and cost bases. You can use RBL to roll up financial data to all joint owners' primary households by doing the following:
Create custom RBL rules to rollup the joint owner balances using the Joint Owner field on the Financial Account object.
Enable RBL rules that rollup balances using Financial Account Role for joint owners using the Account Role field on the Account Contact Relationship object. Verified Reference: : Salesforce Financial Services Cloud Implementation Guide, page 75.

Explanation
To configure a custom field for reporting when relating two-person accounts to each other, the Financial Services Cloud consultant should configure the custom field on the Account Account Relationship object. The Account Account Relationship object is a junction object that links two accounts together and defines their relationship type and role. By configuring a custom field on the Account Account Relationship object, the consultant can capture additional information about how two-person accounts are related to each other and use it for reporting purposes.

A Relationship Group is a construct in Financial Services Cloud that allows you to model complex and dynamic relationships between clients and accounts. You can use Relationship Groups to link duplicate client records and create a consolidated view of their financial data, activities, and interactions. You can also use Relationship Groups to sync data between Salesforce and the source system using external IDs and integration tools. Verified Reference: : Salesforce Financial Services Cloud Implementation Guide, page 67.

The following statements are correct about the Actionable Relationship Center Manager (ARC):
To enable users to see the ARC, you will need to add the component forARC to the page layout. The ARC is a Lightning component that can be added to any Lightning page that supports components, such as record pages, app pages, or Home pages. You can use the Lightning App Builder to drag and drop the ARC component to the desired location on the page layout.
ARC displays up to 5 related lists that have a configured compact layout. The ARC shows a graphical representation of the account-account relationships for a selected record, as well as related lists of other records that are associated with the account, such as contacts, financial accounts, or opportunities. The ARC can display up to 5 related lists at a time, and each related list must have a compact layout configured to show relevant fields.
The Association Type picklist controls the account-account relationship that display in the ARC. The Association Type picklist is a field on the Account Relationship object that defines the type of relationship between two accounts, such as Household Member, Business Owner, Trustee, orFriend. The ARC uses this field to filter and display the account-account relationships for a selected record. You can customize this picklist to add or remove values according to your business needs. Verified References: : Salesforce Help Article 3 : Salesforce Help Article 4 : Salesforce Help Article 5