Well, it might be like polar bears and grizzley bears: They can interbreed, but only a rare few of them are genetically able to reproduce further. Those ones in turn have more children, becoming instantly the dominant genetic strain since there's literally no competition. And unlike bears, these are sapient creatures.
So a halfie born of two halfies is viable, but one born of mixed parentage is sterile.
Well, it might be like polar bears and grizzley bears: They can interbreed, but only a rare few of them are genetically able to reproduce further. Those ones in turn have more children, becoming instantly the dominant genetic strain since there's literally no competition. And unlike bears, these are sapient creatures.
So a halfie born of two halfies is viable, but one born of mixed parentage is sterile.