Написано на сайте болгарского посольства вот это:
:Important Notice!• Family members of EU citizen, who do not have the nationality of the EU Member State, are entitled to the same rights as the EU citizens, for their travel to Bulgaria. This only applies to those having residence in an EU country and travelling together, or going to Bulgaria to join their family member (s) who is (are) already in the country. While travelling alone such family members have the right to enter, but require a visa to be issued by the respective Bulgarian Embassy abroad. The visa is issued free of charge on the presentation of a valid passport, application and proof of family ties (Marriage Certificate or Birth Certificate, legalized and translated into the official language of an EU member country). Family members, travelling together with the EU citizen does not require a visa, but should be in a position to present on request at the border a Marriage Certificate or Birth Certificate, legalized and translated into the official language of an EU member country.