- Baby 5 is from Kuen Village, in the North Blue (likely taken from "kuenai", "can't eat"). She was discarded by her mother when she was still young, which developed a trauma where she does everything possible to feel needed by others
After doing her best to survive, she was eventually rescued by Doflamingo, who treated her as part of a family. It may not look like it, but she's very kindhearted deep down.
Her real name is unfortunately not confirmed and it doesn't look like it's "Baby Five"
- Buffalo was from a country in the North Blue pertaining to the World Government that was under a horrible dictatorship. As part of this rough dictatorship, a practice was enforced by many families to abandon their children in order to lessen the economic costs of sustaining them
This caused many children to become orphans, among which was Buffalo. With other children, he desperately tried to survive in the sewers of the country. Eventually he was rescued by Doflamingo and was brought to an environment that for him, in comparison, felt like a paradise
The reason he got along well with Baby Five was because of their familiar past, as they both were abandoned by their parents and forced to survive