The process to get a Schengan visa short stay for your non-EU spouse in Islamabad is as follows:
Marriage Registration Certificate (yes the English one only) and Birth Certificate of the non-EU Pakistani spouse - need to be attested by the Ministry of Foreign Affairs in Islamabad. (They charge only 10 rupees per document but there are very long queues in place and you will need your Urdu Nika Nama for the attestation - as both the English and Urdu get attested together).
Once attested, get a Statment of Confirmation typed up detailing why you are going to Belgium and book refundable Tickets for you and your non-EU spouse to Belgium.
Next, go to the Belgium visa website, apply and download Schengan application.
Finally, book an appointment with Gerrys in Islamabad:
http://www.belgiumvisa-pakistan.com/fam ... ation.html & take with you 40 Euros to get both the Marriage and Birth Certificates legalized by Belgium (this is a requirement and is absolutly necessary).
If Belgium refuse your application on dubious grounds or don't respond after 15 calendar days, go to the EU's SOLVIT website and submit a complaint. They will take over and get the Belgian's to issue a visa.