You will need to start loooong time ago
Any centaur-like living organism has six limbs. And humans have four. If you want to start from a common ancestor, you need to go back in time even before them. Tetrapods (four limbs organisms) evolved from early bony fishes (Osteichthyes), specifically from the tetrapodomorph branch of lobe-finned fishes (Sarcopterygii), living in the early to middle Devonian period.
The organisms with six limbs evolved from a different and older ancestor (presumably a crustacean). But since Centaurs are really mammals (horses + humans) they cannot fit in that category. Therefore, if you really want to have all of them have something in common, you need to design a different evolution path.
You will need a common six-legged mammal ancestor that evolved from a different type of acuatic prehistoric animal in your world. And then it common ancestor will eventually mutate in different paths according to the environment it evolved in.
However if your Draconic centaurs have wings beside their hands, it will make them 8 limb creatures. So you need an 8 limb common ancestor, and then make it lose a pair of limbs in further evolution stages (the same way dolphins and whales loose their legs). In that way, you can justify the existance of a single common origin for all of them.
Besides you will need the Draconic creatures to be mammals. And then justify the lizard-like appearence (they will end up being something like a pangolins or an armadillos).