generally speaking this is a tricky situation. Whichever option you choose I would consult a laywer to help you with the steps.
Now, in your case I think two problems may come up and the German authorities will likely give you a hard time:
- are the certificates of Pakistan authorities valid ?
- given that your asylum application has been rejected the issue of fake marriage will be scrutininzed (also in view that you divorce will be very recent)
You will have to overcome these hurdles in each option.
Now, not easy to say which way is easier.
I would guess (but this is only a guess) that first marriage in Pakistan and then apply for Familienzusammenführung is the easier process. In addition I would recommend you that your wife then goes back to Germany and lets the Pakistani marriage certificate have registered/recognized in Germany (just for herself) -(-> pls consult a lawyer with experience in recognition of foreign marriage certificates before!) As such you may have a better chance that the above issues (validity of Pakistani documents, fake marriage issue) are no more a major hurdle when you apply for Familienzusammenführung.
I think it will be harder to get the marriage in Germany through (the other option):
- a Pakistani court decision on your divorce (the validity will be checked thoroughly by the German embassy).
- a certicate of no impediment to marriage from Pakistan
- and the Standesamt will check whether it is a fake marriage
@ your question: whether you can come back with your wife immediately with a visa "c"? Well, I would guess if you want to apply for Familienzusammenführung you still need to be in Pakistan (you will also have an appointment with the embassy there). It is not clear to me on which ground you could apply for visa ? (or do you intend to apply to another Schengen state for this visa?)
(Sorry I just realized I have been writing in English even though your German is perfect.)
Bitte zögere nicht weitere Fragen hierzu zu stellen.