I don’t think Daath can physically have more kids. He was told he might not be able to have any in general so the twins were technically like miracle babies. He also struggled a lot during that pregnancy so I doubt he’d be able to have more, but you never know. For the sake of Daath’s health I kinda hope he doesn’t
Like said, it is explained in Pendulum that conceiving and carrying a beast chlid is very difficult.And it seems to be true because Kai got pregnant tardily even if he bonded with Luard when he was 18 (I'm not sure). He gave birth to Sai-chan when he is maybe 23 or 25. Plus, he wasn't infertile like Daath for whom it was a miracle to give birth. So I guess this is not very easy to give birth to a child beast. The pregnancy seem to be difficult too so I when you have one child, maybe it is enough for your body... That's why Dath having twins was also a big deal. ^^

i wonder, why dont they have another siblings? why daato and juda dont have another children? im curious, since juda also an only child.. it is a law or smthg in the beast world? just asking bc i seriously wanna see more little furball