Plumbing – Installing trap with new deeper sink

It's a grey area. Nothing explicitly says you can't, nor explicitly that you can. An inspector could reject it based solely on it preventing the fixture from "draining rapidly". I see your proposal as OK, it's no different than adjacent basins sharing a single trap. As long as the horizontal offset is less than 30" and there is not more than 90 deg horizontal change of direction.

Under such circumstances, no one can predict the result of an individual inspection. You can either enquire in advance, or just do it, having a more conventional plan B should there be any objection.

No, there should not ever be two traps on a single drain line.

The point of the trap is to create a water barrier which prevents sewer gasses from coming up the empty pipe and into the house.

When you have two traps on the same line, you end up creating a kind of vapor block in the line which prevents it from draining properly.

What do you do?

Get yourself some 1 1/2" PVC (not CPVC, which is yellow, PVC which is white) with a 90 deg elbow, and also get two Fernco couplings (black plastic couplings with straps on each end that can be tightened) that will fit the pvc and iron drain pipe.

Use a metal blade on a sawz-all and cut out the p-trap in your basement. (Have a bucket handy!) Leave room to connect the Fernco coupling on both sides. I'd cut the right hand side out just past the coupling.

Measure and cut the PVC so that with the 90 elbow the ends line up with the newly cut drain lines. Glue the PVC together and confirm the fit, then connect to the old drains with the Fernco.

Viola - a proper drain line that will drain smoothly w/ no vapor lock.