Can you switch between Jason and Lucia in GTA 6?
Yes, mostly.
Viral claim: “You can't switch between Jason and Lucia” False
Yes, mostly. Rob Nelson, who co-runs Rockstar North, told Famitsu you can switch control between Jason and Lucia. It only gets locked during some story scenes, the same way GTA 5 handled Michael, Franklin and Trevor.
During IGN's demo he switched over mid-session and said: "Oh, or you can switch and Jason's in the shower!"
The headlines saying you can't switch whenever you want took the story-lock part and dropped the rest.

Watch us check it
Sources
Until launch this comes from pre-release previews and interviews. We re-check every verdict against the real game after November 19 and note any change here.