Houki has a giant 25m Wolf summon, and Metal has a 25m Snapping Turtle summon. Metal has a chief turtle, Houki has a chief wolf.
Once Metal turns 14 he gets his own little turtle summon, around the size of the little S.O.S turtle Gai has, and like how Naruto did, wait until it got bigger and bigger. Until it was big enough to ride.
Metal leaves the turtle in his scarf to carry him around. And when the size of a small puppy, he held him on his head like Kiba with small Akamaru.
Theeeen his turtle got too big to be held on his head. And eventually it grows to a giant turtle summon.
Same thing with Houki. Summons a giant chief wolf at first, then gets his own little wolf pup. Which he takes care of and trains with.
My favorite headcannons is that Houki receives the Hound summons from Kakashi, and ends up with Pakkun's daughter as his main connection summon.
She likes to chill on his shoulder (much like her father) and will rip out the throat of anyone who threatens her favorite human. She met him one day while chilling in Kakashi's Hokage vest while he was walking through the town after a meeting, and as soon as she saw Houki in the crowd she knew she needed to meet him.
So Houki has a deadly super speedy pug who can track his enemies (which is perfect for a kid training under Sai to be an Anbu like operative) and gets the other seven hounds along with her, getting a team much like Kakashi's but also very different since they are the next generation like him.
