Maybe not. It says only human omegas can give birth to beasts.
http://www.mangago.zone/read-manga/pendulum_kemonohito_omegaverse/nmt/c001/26/
But that does leave to question why such a bond is necessary and what female beast do. It may be they aren't viable. It would be adorable if possible. For all that is holy, I hope they don't call her Bella...
http://www.mangago.zone/read-manga/doronuma/
I know who he ends up with
I don't think they can have another child at all. The explanation has slight spoilers for the main series though BE WARNED
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because he took a lot of cheap drugs he lost most of his omega pheromones and couldn't have heats. You can also see that he got a cesarean in this spinoff. He vaguely hinted that it was impossible to give the twins siblings. These twins are actually a miracle born from ~LOVE~ if you think about the situation.

I kinda want them to have another baby... like a little girl... idk why but that would be so cute!!