Twist #2: Shaun actually did die in the conflict and the game is about the parent learning to accept it.
Twist #3: (if you're playing the dude) You were Shaun the whole time. Turns out the 'make the baby look like the parents' was taken very literally. Congrats! YOU ARE YOUR OWN SON!
Twist #4: Shaun, the biological child of Howard/Nora did die. The game is actually centered around a child/young man named Shaun who becomes Howard/Nora's surrogate child.
Twist #5: Shaun is reveled to have left to the Capitol Wasteland years ago talking about the evils of a great, fat worm.
Twist #6: Shaun had become a Super Mutant who thinks he's Uncle Leo. That's right. That Uncle Leo.