I live in Florida, slab home and I'm adding a tub and laundry room. I would like to use a single 2" vent/drain combination to wet vent a 4 fixture bath group. Sketch is attached. My questions are:

1) Is the drain 1.5 to the p-traps then 2"?

2) Does the 3" drain transition to 4" at the exiting clean-out?

3) Can the wet vent be on the last fixture downstream?

4) The length of run is unlimited if proper drop is maintained?

5) Do I wye into the existing 4" drain with a wye and rubber collars?

Thanks for your help...

Greetings from Sarasota,
1) Is the drain 1.5 to the p-traps then 2"?
No the drains and traps are 2" to the tailpiece of the fixture. The 2" trap will use a 2 X 1 1/2" nylon gasket to pick up the 1 1/2" tailpiece.

2) Does the 3" drain transition to 4" at the exiting clean-out?
Here's where it gets confusing. You don't have a toilet to go with the tub/shower? Anyhow check your local code. In Manatee county I can use 3 inch under the slab but Sarasota County holds me to 4 inch.

3) Can the wet vent be on the last fixture downstream?
Get ready for a truckload of bad news. In technical terms, your plan sucks!!
EVERY fixture that has a trap MUST be trapped.
The only fixture in your plan that can be wet vented is the tub. And the tub must be wet vented back to a drain line of a fixture that has its own vent. The other fixtures MUST BE VENTED, however, the vents may be tied together and revented back to a dry vent in the attic.

4) The length of run is unlimited if proper drop is maintained?
True, 1/4" to the foot slope.

5) Do I wye into the existing 4" drain with a wye and rubber collars?
You cut into the main with a No-Hub wye and connect with Fernco Banded couplings.

Vent the other fixtures and check the code and you're good to go. Good luck, Tom