One thing I read on a reddit thread [1] was that the AI pro 2 TB plan explicitly allows sharing the AI and storage benefits when you enable family sharing on them, while the 5 TB plan doesn't.
However, when I went to sign up, the 5 TB plan wasn't available at all! It's only their lite and basic plans (the one with 30 and 100 GB of storage); the 5TB one only showed up after I signed up for the pro plan, and judging by how the UX looked, you pay an extra amount on top of your AI pro plan.
Now I definitely need family sharing, but I don't need the full 2 TB, let alone 5 TB, so I didn't bother checking further about the 5TB plan.
Also, I am in India, maybe things are different in your region?
[1] https://www.reddit.com/r/GoogleOne/comments/1nib21a/solved_g...
The difference between the AI and non-AI 2TB plan is 1000 AI "credits" (tokens?) vs 200. €120 p/a difference between the two for me which is huge.