Your best bet is to start on easy 'Cakewake' mode and play through several times.
Stick to the same characters throughout until their trust achievement unlocks.
Apart from Bo you can start at chapter 2.
Don't forget with the monkey chapter 2:5 you need to select the two characters you don't want to boost with initially as they will go up in the lift in advance leaving you with the two you do at the monkey bit at the end. I got Rachel at this stage.
Much easier if you play without the mike and just make responses with the buttons. If you answer incorrectly or accidentally shoot the character you are trying to gain trust with just reload checkpoint.