My great great grandfather was born in 1869, and his listed birth place on his marriage certificate is Mercato. I have his baptism record, which was recorded for canonical purposes, which I received from the Archdiocese in Naples and I found his marriage certificate on Family Search microfilm files.
For purposes of obtaining dual citizenship. How do you obtain a birth certificate of an orphan?
How to obtain a birth certificate of an orphan?
Re: How to obtain a birth certificate of an orphan?
Can you tell us the name of your GGGF, a link to the marriage certificate, and post the baptismal certificate?
Emilio Lussu: “Che ne sarebbe della civiltà del mondo, se l’ingiusta violenza si potesse sempre imporre senza resistenza?”
Slava Ukraine!
תחי ישראל
Slava Ukraine! 
תחי ישראלRe: How to obtain a birth certificate of an orphan?
You should contact people who are knowledgeable in this field so they can advise you specifically and in detail.