Hello all. Previous owners had connected (incorrectly I think) a double sink vanity to the existing drain. They simply glued a tee and a few elbows to the wall inlet (no slip fitting) and ran the drain pipe to the second sink through the cabinet.
The only thing incorrect about that was the extra elbows and perhaps the use of the wrong sort of "tee" fitting.
Indiana has apparently adopted the 2018 IRC including the plumbing sections, but is still on the 2006 IPC. Homeowner's get a choice of whether to following the plumbing sections of the IRC or the IPC.
Either way (assuming the 2006 IPC is like current IPCs, I didn't confirm), both codes allow what they call "common venting at the same level". That means two trap arms may connect prior to either one being vented, and then the joint drain may proceed to a common dry vent for both of them. Each trap arm individually, from trap to the common vent, must comply with the length and fall limits on trap arms.
So if in your picture above the san-tee is a dry vent, and both sinks are on one side of that stack, you can common off the san-tee with a common drain for both sinks. Then you'd hit a 1-1/2" combo in a horizontal configuration for the stub-out for your first sink, and continue horizontally to a LT90 for the stub-out for your second sink.
Cheers, Wayne