New Bath - Drain and vent

[wis_diy-er]

Blue = Existing Vent,
Black = Existing 3" Drain
Red = New plumbing
Need to add 2nd story lav sink. Can I do a wet vent from the new lav sink to the exiting lav sink on first floor? If so, do I need to, or should I remove the "dashed" line i have in image?

 

[breplum]

If you bring the new lav drain down to tie in below the existing lav p-trap, then it is not a wet vent anywhere.
It is just a drain connecting to a drain.
The common drain should be a 2" pipe if two lavs are accounted for. Though, in reality, due to normal odds, the simultaneous flow from both would rarely occur, but the code always errs on the side of caution.
Do not remove the existing lav vent, it is doing its job (if the lave is still there).
If the main floor lav is removed, then of course you don't need that vent.

 

[wis_diy-er]

Thanks for your reply Breplum,