- Your drawing is unclear, because sometimes you are using up/down the page to be mean vertical (the 2" vent, the stack), and sometimes you are using it to mean horizontal (presumably the sink and tub don't drain upwards). So how about a proper plan view drawing, where both directions are horizontal, and a vertical stack or vent is just represented by a circle, its cross section.
- How are the existing WC and tub vented? If the stack has no fixtures draining in from above, and the stack is the only vent, with the WC and tub drains combining together to before joining the stack, that's possibly OK. The IPC allows common venting like that; the tub trap arm from trap to stack (ignoring the WC) has to meet the usual rules, namely that it falls less than one trap diameter, while falling at a rate of at least 1/4" per foot.
- If the existing WC and tub are common vented, then you can't join your new drains into the stack at that level. Common venting is limited to 2 fixtures. You can join them into the stack at a lower elevation.
-The new bathroom sink will need a dry vent, as it has the highest elevation trap. The dry vented sink can wet vent the shower and the new WC.
Cheers, Wayne