These things were more or less shown at the end of the manga after the time skip, so I feel like you are given GT way too much credit. They more or less based their personalities based on Toriyama's own vision. They unfortunately didn't really build upon it in a meaningful way. Especially Goten wasn't utilized at all in GT and became an irrelevant and unlikable side character. But as everyone knows, GT stands for Goku Time. And there is no point in having this Gohan discussion again.