My wife needed her grandfather's birth, marriage and death certificates, her mother's birth, marriage, and death certificates, and her birth and marriage certificates.
Interestingly, because she did it before having children, we were able to get Irish citizenship for our children as well. For them all we needed was my wife's certificate of foreign birth registry, and their birth certificates.
Yes, it was very involved and all documents need to be official. raised sealed or raised stamped documents. No photocopies or other.
I needed: My birth certificate, my marriage certificate, my divorce decree, name change (back to my maiden name) document, my mother's birth cert, my mother's marriage cert, my Mother's death cert, my Grandmother (my Mother's Mother) birth cert, my Grandmother's marriage cert, my Grandmother's death cert. Also, a notarized copy of my passport, a form witnessed by a lawyer, bank officer, police officer or clergy attesting to knowing me (I chose my own lawyer) with their business card, copies of bank statements, utility bills and a few other incidentals. It took a year.
Note: My Grandmother's birth cert was a long form. Baptismals certs are not acceptable. If the birth cert was not registered, there is a form that can be requested and can be submitted in lieu of.