So, any headcanons for the pups that didn't get that much characterization, for example, the Dimitri triplets, Delgado, and the twins Dizzy and Dee-Dee.
Some, but I'm saving a lot of them for the story! If you want some quick little ones though...
The Dimitri's are troublemakers, but they just kinda wind each other up and make their behaviour worse. Pack mentality and all that. They really do mean well and don't want to hurt anyone... badly, but they're also just used to only trusting each other and thats hard to unlearn. I think they, deep down, don't feel like members of the family a lot of the time. (Spoilers, but they are about Dante and Dawkin's age. So they ain't being born into the family.)
Delgado, for all his need for speed, hates the smell of any kind of smoke. Just makes him nauseous. So don't ask him to burn any rubber!
Dizzy and Dee Dee, canonically, have spots and markings that bar them from Dalmatian Kennel Club breed standers. That gets them look down upon by upper crust dogs. (Any breed trait deviation dose.) Thankfully the family don't run in those circles, so the girls don't get any issues about it.. once they get older though, they may find the world a bit meaner in places then they were expecting. Thankfully Dolly and their mum have instilled enough confidence for them to get through it just fine!