I still think that
Stephanie Cegielski was telling the truth when she said that Trump didn't actually plan on getting as far as he did, and I think the rest of the Trump clan felt the same way. But then suddenly momentum built up faster than they were expecting and the Trump ego took over, and they were all in way over their heads.
I think this makes it especially tough for Jr. and Eric, who don't seem to have any interest in political stuff at all. They just want to continue their jet-setting, rich-guy lifestyle, and politics and the actual requirement to at least appear to have some sort of conscience is really cramping their style.
I don't particularly feel sorry for them, as they could have stepped aside at any point earlier in the game, but I do feel a tiny bit bad for them. They're like toddlers who have only known one way of life (and always gotten ice cream whenever they wanted), and now things have changed dramatically, including people slapping their hands when they go for the ice cream. They grew up thinking the world worked how they wanted it to, and they're learning that not everything is the same outside of their little rich-guy world.