The account's owner invites agents from Setup › Team with a link that works once, for a week. Each agent signs in as themselves.
A lead belongs to the agent whose lead address received it. Each agent's clients and pipeline are their own while they are on the team. The owner sees the team's totals, counts only, and every lead.
When an agent leaves, their clients stay with the team. Each agent who sees MLS listings needs their own CRMLS ID.