Not much is known about what they do in Kano Country, but the two members seem to be very loyal to their leader and grandfather, Don Chinjao.
Members of the family have a blood relationship with each other. Sai and Boo are the grandsons of Don Chinjao who is the head of Chinjao Family. All three of them are (or in Chinjao's case, was) in the Happo Navy, and specialize in the Hasshoken (八衝拳 Hasshō-ken?, literally meaning "Eight Impacts Fist"), a fighting style that imbues vibrations in a strike to break the enemy's armor and weapons, similar to Whitebeard's Gura Gura no Mi.
In the past, their leader was a fearsome pirate, worth over 500,000,000. After Monkey D. Garp dented Chinjao's pointed head, robbing him of his power and the means to acquire his fortune, Chinjao swore to get revenge on Garp and his family.
During the Dressrosa Saga the group traversed to Dressrosa, ostensibly to compete at the Corrida Colosseum for the Mera Mera no Mi. Their true purpose, under orders from the king of the Kano Country, was to investigate and cripple a weapons trade that the Donquixote Family managed, whereby Doflamingo sold weapons to warring nations, including those opposing the Kano Country.
After they arrived and signed up, all three were placed in C Block. Later, during B Block, Chinjao met with Monkey D. Luffy, the grandson of Monkey D. Garp, who was also competing in C Block. He attempted to kill Luffy before the match, but Sai and Boo stopped him. Chinjao planned to kill Luffy during C Block.
During the battle royale, Boo was defeated by the Funk Brothers and Sai was later knocked out of the ring by Luffy. Chinjao and Luffy then became the last two contestants during this round. After a fierce battle, Luffy overpowered Chinjao but also inadvertently restored his pointed head.
After the match, Chinjao was appeased and he ceased his desire to kill Luffy. Sometime later, they were tricked and thrown into an underground dungeon along with the other disqualified participants. Sai and Boo were soon abducted and transformed into toys while Chinjao lost all memories of them.
Sometime later, Chinjao was turned into a toy as well and the Chinjao Family was forced to work as slaves in the underground trade port. When Sugar lost consciousness, her curse broke and the Chinjao Family returned to being humans again.
During the battle to overthrow the Donquixote Family, Boo fought and was defeated by Machvise while Chinjao engaged Lao G in battle and Sai was fighting with Baby 5. As Sai fought with Baby 5, she misunderstood his threats as flirting, which greatly confused Sai. Later on, Chinjao became distracted from his fight with Lao G and told Sai he was against his union with Baby 5 but his grandson retorted he was not going to get married. Baby 5 then asked Sai how she could be of use to Sai, which he sarcastically said he wanted her to kill herself. Baby 5, taking him seriously attempted to kill herself, thinking she could be useful. Sai attempted to stop her, which infuriated Chinjao, because he detested saving enemies. He went to attack Sai with Drill Nail, but Sai countered with Bujaogen, which bent Chinjao's drill head. After this, Chinjao realized Sai had awoken his power, he bestowed the Hasshouken Secret Technique: Drill Dragon to Sai, and giving him full power over the Happo Navy. Chinjao was about to tell Sai how proud he was of him before a much larger Lao G attacked him and knocked him into a wall defeating the old pirate. Lao G then set his sights on Sai calling him "a monkey from the Kano Country" and told him he can't have Baby 5 while referring to her as "convenient" hurting her feelings. In response to his grandfather's defeat and Baby 5's honor, Sai retorted if he won he'll make Baby 5 his wife which elated her feelings. Sai then use the Hasshouken Secret Technique: Drill Dragon Nail for the first time and with it he defeated Lao G whilst shattering the ground. Lao G then called Sai a "Stupid Monkey" to which Sai retorted "Call me Don".