I fail to see the cause for suspicion that Kaido would want to save Ace, all because Ace met Yamato. The suspension of disbelief here would be unreal. In order for this to be the case, we have to assume that Yamato (Is in fact a girl) fell in love with Ace, they developed a relationship in just a couple days, that Kaido approved of, and now looks at Ace as his son in law. Then Kaido, for some inexplicable reason allowed for Ace to leave the Country of Wano, instead of having him join his crew, which Ace should have been more than happy to have done considering his new found love for Kaido's daughter. And that's just the tip of the iceberg, not even touching the relationship between Luffy and Shanks and the fact that Luffy and Ace are brothers.