You do believe in common ancestory in some sense though, don’t you? i.e. the domestic dog and the dingo are descended from gray wolves. So dogs and dingos have a common ancestor.
(Granted, they are all the same species, just different sub-species, but it’s the same concept.)
It’s not like there were no dogs and then poof, there were 2+ dogs. It’s not like 2 wolves gave birth to a pug for example. The first dogs were very wolf-like. And they could breed with wolves, so they did not need more dogs around to breed with. To go further back: the ancestor to the gray wolf is
Canis lepophagus - a different species. But it’s not like Canis lepophagus gave birth to the first wolf. The first wolves were very lepophagus-like. I assume they were close enough that they could breed with the lepophagus.
Speciation is very gradual. So no, the male and female of a species do not need to be created simultaneously. They breed with other ones around them.
Say some humans have essentially domesticated some wolves, and named them Daisy, Daffodil, Spike, and Spot. They were the cutest and nicest of the ones around. The humans breed Daisy and Spike, and they have a litter of pups, and their pups are really REALLY nice. They are so nice, they can be considered dogs. They wag their tails and “woof” instead of howl.
Spot and Daffodil have a litter but their pups are just average nice. They are just nice wolves, not dogs. They howl, they don’t woof. They let the humans pet them, but they don’t get all excited and joyful like Daisy and Spike’s pups. But the pups from Daisy and Spike’s litter can still breed with Spot and Daffodil’s litter.
On and on they got nicer and nicer and cuter and cuter so that Daisy’s, Daffodil’s, Spike’s, and Spot’s great great great great great great great grandpuppies are so nice and cute, they would not be mistaken as nice wolves, they really are dogs.
Other great great great great great great great grandpuppies of Daisy Daffodil Spike and Spot became dingoes though when their human owners brought them to Australia.
The same thing happened with their ancestors’ ancestors’ ancestors’ all the way back except their ancestors developed from natural selection, not human selection.
So just think of how different pugs are from wolves - it only took ~13,000 years for wolves to become pugs. Imagine how dramatic changes could occur given millions of years - surely enough to make the common ancestory of canids, felids, and other mammals believable…
If you have trouble believing that, say, cows and jellyfish have a common ancestor, I can understand that. But it shouldn’t be too hard to believe mammals having common ancestory. And once you accept that…the rest starts to make sense too.