Jeff admittedly found his new father to be rather attractive and didn't want to ruin that by changing her too much. So he left Amber with her female body for the most part. The only big change would be that she would grow a very large, thick cock and a pair of huge balls, out from her clitoris, replacing it entirely. Now with a futanari father and a scheduled to soon be female mother, all that is left is to add a special bit of flare.
To accomplish this, Jeff turned them both into living goo/slime. They would be fully able to maintain their body shape and size. And also able to physically interact with things as if they were normal humans. However, both could liquefy any part of their body, collapsing into a puddle even, at the drop of a hat. They could then return to their standard appearances, or something different. Both would have a preference for their human appearances though. They can change their body color too. Amber would become amber colored slime, while Jeff set Gabrial able to turn into a violet purple slime. When like this, anything inside their bodies would be visible, including what they ate, anything they shove inside themselves, and even the after effects of their sex, and the cum still inside Amber's balls.
Now that both of his parents, and his sister are taken care of, all that's left to change, is himself. Jeff thought pretty hard about this and finally decided on...