Carmen is a Spanish name that means song or poem—its big claims to fame are a fabulous opera (you've definitely heard some songs from it!), and Carmen Miranda, a vintage film star and salsa singer, and the more modern Carmen Electra (Prince was the one who dreamed up the name for her—her original name was Tara). It's still in the top 400 baby names in the U.S.
Gabriela is a feminized version of Gabriel, which means "God is my strength." The more popular spelling of the name is Gabriella—that's in the top 50—but the one-l version is just as lovely, and just outside the top 200 baby names.
What do you think of Alec and Hilaria's choice?