What often happens currently is number 1, but usually minus the first sentence:

The specific ones gets closed as a dupe of the general one, but no clarification of the specific point happens.

So my preferred approach would be your number 1. I'm not too bothered which order it happens - so closing as a dupe and then adding or editing an answer will also work - but I think this makes the most relevant information available in one place on that topic.

Where both questions already have answers, closing as dupe and then merging works well, as you end up with one question, and all the answers from both,