The Yonko Kaido's crew in One Piece, the Beasts Pirates, is a massive one, enough that his organization is capable of running all of Wano Country by proxy from his fortress, Onigashima. It's implied that there are thousands of members, split into various ranks, making them one of the most formidable fighting forces in all of One Piece. At the bottom are the Waiters, low-level foot soldiers who have not yet been deemed worthy to consume the artificial Zoan Devil Fruits known as SMILEs. Above them are the pleasures, who ate SMILEs, but failed to gain any powers.
When an individual eats a SMILE fruit and fails to gain any abilities, they are left with a permanent grin on their face, regardless of their emotions. Above the Pleasures are the Gifters, those who gained various animal forms as a result of eating SMILEs. The strongest Gifters and a few other elite crewmembers have risen to the rank of Shinuchi, and hold various powerful positions. Examples include Babanuki, the warden of Udon Prison who ate an Elephant SMILE, and the notorious pirate fortuneteller Basil Hawkins, whose crew was subsumed under Kaido's after he defeated him in battle. Only 9 individuals rank between the Shinuchi and Kaido himself. These are the Tobiroppo, or Flying Six, and the three All-Stars.
Who Are The Tobiroppo?
Each of the Tobiroppo are among the strongest of Kaido's crew, and are given wide authority over lower-ranking members. Each member has eaten an Ancient Zoan Devil Fruit, which allows them to transform into an extinct animal.
The first of the Tobiroppo to be introduced, although he hadn't yet joined at the time, is the former Marine Rear Admiral X Drake. Like Luffy, Zoro, and Hawkins, Drake was one of the 11 Supernovas on Sabaody Archipelago prior to the time-skip. After the timeskip he becomes a spy and joins the Beasts Pirates, but his activities are discovered, and he defects and joins the Straw Hats in their allies in attempting to defeat Kaido. Drake ate the Ryu Ryu no Mi, Model: Allosaurus, and regularly uses a four-bladed axe and rapier in battle. He has the lowest bounty of the Tobiroppo, at 222 million berry. The next to be introduced is Page One, who ate the Ryu Ryu no Mi, Model: Spinosaurus. Page One engaged with Sanji in Wano's Flower Capital, which eventually resulted in a stalemate and Sanji's escape from the city. He managed to defeat Nami and Usopp before he was eventually taken down by a Haki-infused punch from an angry Big Mom. Page One's bounty is 290 million berries.
Page One's elder sister Ulti is also a member of the Tobiroppo. She fawns over her brother constantly and frequently asks him to pamper her, much to his annoyance. Ulti ate the Ryu Ryu no Mi, Model: Pachycephalosaurus, and consequently has an extremely power headbutt. At Onigashima, Ulti fought Luffy before the battle was interrupted by Yamato, Kaido's biological daughter. She then fought and helped Page One pursue Usopp and Nami before being temporarily taken down by a blast of fire and lightning from Big Mom. After regaining consciousness, she continued to pursue Nami but was eventually defeated by the latter. Ulti's bounty is 400 million berry.
Sasaki leads a group of Gifters known as the Armored Division, prized for their high defensive capabilities. In line with this, Sasaki ate the Ryu Ryu no Mi, Model: Triceratops. Sasaki fought and eventually lost to Franky on Onigashima, losing when the latter's Radical Beam hit his belly, his only weak spot. Sasaki's bounty is 472 million berry. Black Maria runs her own brothel on Onigashima, and is by far the largest of the Tobiroppo. She dresses like a traditional Japanese oiran, and is a skilled shamisen player and singer. Black Maria ate Kumo Kumo no Mi, Model: Rosamygale Grauvogeli, which allows her to transform into a giant spider. Black Maria pummeled Sanji on Onigashima due to the latter's refusal to harm women. She attempted to use Sanji as bait to lure out Nico Robin, who Kaido wants to capture. Sanji places his trust in Robin, who eventually dispatches Black Maria. Black Maria's bounty is 488 million berry.
Who's-Who has the highest bounty among the Tobiroppo, at 546 million berry. He was once a member of the World Government assassin squad CP9 but was imprisoned for failing to guard the Gomu Gomu no Mi, which Luffy eventually ate. Who's-Who ate Neko Neko no Mi, Model: Saber Tiger, and is also able to use all of the Rokushiki techniques used by CP9 members, and is said to have similar power to CP9's former strongest member Rob Lucci (now a CP0 agent). Who's-Who is eventually taken down by Jinbe.
Who Are The All-Stars?
The All-Stars are Kaido's three strongest crew members. Like the Tobiroppo, they ate Ancient Zoan Devil Fruits, but their power is substantially higher, with all three having bounties in excess of 1 billion berry.
Jack is the first of the All-Stars to be introduced, when he attacks the Mink Tribe on Zou, eventually being driven away. Jack fights quite a few individuals over the series, including the renegade samurai Ashura Doji (who proved outmatched and ran from him), and the Mink Tribe leaders Inurashi and Nekomamushi, who fought him on several occasions. It was Inurashi who finally took down Jack for good. Jack ate the Zou Zou no Mi, Model: Mammoth, and wields a pair of twisted blades when in his human form. His bounty is exactly 1 billion berry.
Queen rules Udon Province in Wano, and is the Beasts Pirates' pre-eminent scientist and mechanic. He has upgraded his own body with a litany of cyborg parts. Queen ate the Ryu Ryu no Mi, Model: Brachiosaurus. At Udon's Prisoner Mine, Queen was easily overpowered by Big Mom. He later fought Chopper, but failed to defeat the Straw Hat's doctor until Big Mom's eldest son Perospero intervened on his behalf. Queen was eventually taken down by Sanji's Boeuf Burst. Queen's bounty is 1.32 billion berry.
Second only to Kaido in strength is King, with a bounty of 1.39 billion berry. King is one of the last-surviving members of the Lunarian race, who possess the ability to generate and control fire. King also ate the Ryu Ryu no Mi, Model: Pteranodon, which allows him to fly. King's Lunarian physiology makes him almost impossible to damage. He fought the former 1st Division Commander of the legendary Whitebeard Pirates, Marco the Phoenix, to a standstill, and nearly defeated Zoro until the latter figured out that he becomes faster but weaker when the flames on his back disappear. Zoro took advantage of that knowledge to defeat King, leaving Kaido as the only major in the Beasts Pirates left standing as of this point in the story.
As of the current point in the story, the Tobiroppo and All-Stars, except for Drake, all lie defeated. What will happen to them in the aftermath of the Wano arc is still a mystery, but one worth discovering the answer to.