Do Jason and Lucia mean GTA VI has two-player co-op?
Two protagonists do not establish co-op. The current product listing describes a single-player experience.
No co-op or cross-play announcement was found in the product pages reviewed. Future online plans are a separate question.
The evidence
No announcement found in the sources checked on the verification date.
Take-Two InteractiveJune 24 preorder announcementRead the full supporting guideWhat would change this answer?
A Rockstar announcement identifying co-op, multiplayer or cross-play support.