So, Twi'lek hybrids have appeared in Star Wars Canon in two mediums. The animated Clone Wars and the recent live-action Ahsoka TV series. In the Clone Wars, a clone trooper deserts and marries a pink Twi'lek female. He is able to produce two children who look mostly like Twi'leks except for a few subtle differences. The boy has eyebrows which full Twi'lek males lack and the girl has mottled skin. However, they look mostly like Twi'leks.
Now we look at the hybrid, Jacen Syndulla, son of Human Jedi Kanan Jarrus and Twi'lek mother Hera Syndulla. Jacen looks FULLY human except for his hair color (which is green) that reflects his mother's skin color and is a hue that baseline humans cannot have naturally.
My question is. Why such glaring differences? Is it like here on Earth, where biracial children's looks depend solely on the roll of the die? But they are the same species? Humans and Twi'lek are separate species that evolved convergently, but on different planets. Would hybridization imply that Twi'leks and humans are actually the same genus? Are the Lawquane children and Jacen sterile?
Also, there is evidence for NO external medical genetic tampering. The clone deserter did not have accessed to advanced technology on Ryloth (Star Wars doesn't do that type of stuff usually, and Genetic engineering is mentioned to be illegal in the Mandalorian Season 3) and Hera did not know she was pregnant before Kanan died. They were obviously sleeping together but had no plans to start a family.