Any wet venting has to be on the same floor, a bathroom group in a residence.
The toilet vent, or wet vent needs to happen before the waste from upstairs enters the line.
So the downstairs lav would need to wye in closer to the downstairs toilet, "before" the wye for the upstairs bath.
Also, the upstairs shower needs a vent between the it's trap arm and the stack below the toilet.
The vent needs to come off the top of the trap arm, you can't go up after a vent, except for the normal 1/4" per foot grade, within five feet.
Longer then that, not allowed
More grade then that, not allowed.