I think it's said beast are all male alpha & beta, that's why they need human omega so they can produce offspring. As we can see all omega in mansion are human not once beast
The only female alpha we've 'seen' has been Kai's mother (in the Pendulum manga) she could have been beta, but considering her attitude, probably not. I think any female beast alpha is probably going to be sterile. Beast omegas are probably also very rare and also sterile. Beta seem to have the largest fertile population.
It's because they don't have beast alpha female that they have to mate with a lot of omega,
I do wonder, are there any Beast Alpha that is Female that belongs to their noble family. I also wonder if Shaia is female or male......