They have no set physiology, not even size-wise. The result of breeding a demon to a female mortal is almost completely random except for the fact that it will be a humanoid. Scales, claws, horns, tentacles are common features.
Most of them will not age and can reach thousands of years.
They have none to speak of. They will even avoid one another. On a rare occasion, some might unite in a conclave with no true stability.
As a whole, they are feared, greatly feared.
Most of them tend to hate demons, often becoming demonologist to control them, but some will seek their sire or simply ally with demons, seeing those as the only ones truly like them.