Comments:
1) In the upper left, the drain between the lav vent take-off (san-tee) and the WC will need to be 2" to allow it to wet vent the WC.
2) It's unusual to use a 3" trap for a shower. If you do, it does increase your allowable trap arm length (from trap outlet to vent connection) from 5' (for a 2" trap) to 6'. The vent connection would be the connection of the 2" lav drain.
3) Unfortunately, horizontal wet venting is limited to one bathroom group at a time, and while the definition of bathroom group includes a shower plus a tub with or without shower over it, it does not include 2 showers. So unless exactly one of the two showers is actually a shower over a tub, you can't wet vent both showers via the single lav dry vent.
So the downstream shower would require its own dry vent. It could then be routed separately from the other lav/shower, and either one of them could join the WC drain to wet vent it
4) The WC needs to be vented (via connection of the drain wet venting it) within 6' of developed pipe length from the closet flange. As some of the pipe length will be vertical, that means you can't have 6' horizontally from the closet flange to the vent connection.
Cheers, Wayne
P.S. As presumably there's a wall between the two showers, you could instead take a dry vent connection off the leftward shower trap arm where it passes under that wall (hopefully reducing that trap arm length to 5' or less, so you can use the typical 2" trap), and then keep its drain separate from the rightward bathroom. [Or route it up to the upper 3" drain, but presumably that requires cutting more concrete.] That way the rightward lav could wet vent its shower and WC.
