When Alex finds out how her brother made sure only she could find their grandfathers guitar; he set up a wall of numbers that only Alex, who has synesthesia, could possibly understand the meaning of.
As for Kyle, his motivation through the whole game is to get medicine for her sick sister. He is willing to break curfew and lots of other laws to help her.
Arguably, the ending of the first part. Yes, even Officer Maxwell has a heart somewhere deep down. All it takes is music to make him hold back and let our heroes escape. Makes you hope that maybe you'll be able to save him at some point.