I've read the previous posts regarding this conversion, and I'm hoping to get some expert advice on my specific problem. I'm converting my master bath single vanity to double vanity, and the new double vanity has drawers in the middle preventing me from using a common drain on a single p-trap (that would've been too easy). Please see the below photo of my current (less than impressive) plumbing:

The cutout section is between two studs, and the 2" drain is right up against a stud. The vent goes straight up the wall and to the roof from here. I have no idea what the 3/4" PVC duct-taped to the 2" drain pipe is for??

I'm looking at two potential ways to get where I need to be to have two drains for my two sinks.

Option #1 - 45 degree bends to allow use of double fixture sanitary tee

Option #2 - stacked sanitary tee

I will need to go through the stud on the right side with both the drain and supply lines for the second sink. My two questions:

#1 - What is the 3/4" PVC for? It comes out of the slab and goes straight up, but does not exit in the attic.

#2 - Which of my two options is the better choice? Are both bad?

Also, any additional concerns/considerations?

Your advice is greatly appreciated!