All customers are on a Customer Community License. Universal Containers needs to grant a subset of their customers, known as affiliates, access to other customer Accounts.
What is the most efficient way for the Salesforce Admin to fulfill this
requirement?

Feed tracking and use customs objects record fields and post them as an update. Feed tracking detects that user follows record and update their view of What follow.

Explanation:

Feed tracking is available in Sales Group, Professional, Enterprise, and Developer.

Custom Object is a set of records that allow you to store additional data in an account record and link the data to contact.

Create a custom object in Salesforce

// Created Custom Object and Custom Filed

answerthe reference of the object;