Genetics is real BUT as a student of sociology, it’s the society/ surroundings that moulds an individual.

Sonny experienced things that made him real tough. His kids on otherhand most likely didn’t and just like a lot of mob kids- people probably were scared of their father and pretended to be nice to them. So they grew up privileged in a way and most likely even threw their weight around using their dad’s name

Then when the going gets tough we find out what they’re really made of ... as we have seen