One work by two authors

Use both authors last names, see these examples:

• Parenthetical citation:  Advertisers monitor social media and blogging activity as a way to gauge the impact or lack of impact of marketing campaigns (Tirunillai and Tellis, 2023)
• Narrative Citation: Tirunillai and Tellis (2023) studied the impact advertising on user-generated content such as blogs and reviews.  

One work by three or more authors

Abbreviate the rest of the list with "et al." (Latin for "and others"), see these examples:

• Parenthetical citation: A pilot study of patients with Borderline Personality Disorder showed improvements in emotional regulation through a peer-led art therapy group (Jewell et al., 2022)
• Narrative Citation: Jewell et al.(2022) investigated the use of peer led art therapy treatments for patients with Borderline Personality Disorder, improvements were shown in their ability to emotionally regulate.