In order to get permission for family reunification, you have to lodge a written application to the Agency for Refugees which issues such permission.
Documents certifying the marriage and the children’s birth, if you have them with you, have to be attached to the application. If you do not have these documents, you have to attach a declaration with the names, the dates of birth and the whereabouts of the members of your family (state and address) which must be certified by a notary.
After you receive the permission for family reunification, the Bulgarian authorities will send this information to the Bulgarian embassy in the country where your family is. Your family will have to go to the embassy in order to have a visa stamped on the passport. If your family members do not have passports, the embassy can issue them Bulgarian travel documents (laissez-passer) which will allow them to travel to Bulgaria.
If you do not know where your family is, you can ask the Agency for Refugees to take actions for tracing them. In this case the staff of the Agency for Refugees will approach the UN High Commissioner for Refugees and the Bulgarian Red Cross for assistance in tracing the family outside Bulgaria.