Bathroom Venting Question

I also posted this in the DIY forum...not sure which was more appropriate...

I'm expanding a small bathroom (by adding what was a small bedroom) to make a large master bath.

I've tied into the existing 3" drain. which has a 2" vent stack where an old sink used to be. I've removed the sink but kept the vent.

I'm also adding a tub and double vanity (see layout and photo) to the original 3" drain.

My question is: per the 2012 ; do I need additional vent stacks? If so, would creating a 2" vent above one of the vanities be enough?

Thanks.

Eddie