Although the One Piece family theater was different, Oda replied this way :
O: “Family” has been aired on TV, and it seems to be the most popular out of all the character songs. I really love it, too. My answer would currently be something like this.
- Dad: Franky (Thug)
- Mom: Robin
- First Son: Zoro
- Second Son: Sanji (Punk)
- Daughter: Nami
- Third Son: Usopp
- Fourth Son: Luffy
- Youngest: Chopper
Brook wasn’t introduced in the manga at the time this question was asked. He’d probably be an old perverted grandfather…