Even though they are psychopathic, there are always certain people they would hesitate to kill.
Like Jeff for example. He would hesitate to kill/hurt his brother, Liu and his parents. Although, he did kill his parents and Liu when he first snapped, he regretted doing it. When Liu came back, Jeff sobbed on him and apologised for hours.
For BEN, it would be his brother, Link. Although Benjamin (before the lake incident) did not kill/hurt his brother, Link, his father killed him after he found out that they both stole a Legend Of Zelda: Ocarina of Time game. BEN soon met his brother, who has become Dark Link, by accidentally choosing the same victim. They killed the victim together.
For Toby, it's her mom and sister, Connie and Lyra. Usually, he would take the abuse when he's around and gets upset when he sees it happening to them. After Lyra died in the accident, he got closer to his mom. After killing his dad and fleeing to the forest and became a proxy, he actively avoided his mother in case she doesn't remember him/hated him. Toby would never harm his mother.
For Masky, Hoodie, Tim and Brian, it would've been Jay, if he was alive. There are rumours in Rosswood about a Skull-Masked man running around the forest, and they have their suspicions about it being Jay and the Operator revived him, but they haven't checked yet. If it was Jay though, Tim would get emotional and Brian would probably be surprised. They both, even as Hoodie and Masky, would hesitate and won't kill/hurt Jay, even if he had another 'person' (Tim: Masky, Brian: Hoodie), unless it was absolutely necessary.
For Eyeless Jack, it would be Sally. He doesn't really remember what happened before the sacrifice, so it would be Sally. Being honest, no one would harm Sally. She's too precious.
Clockwork would probably be the same as EJ. She doesn't like her parents, brother or ex-boyfriend.
Jane wouldn't hurt her parents but of course, Jeff killed them.
Sally wouldn't kill/hurt anyone unless they mess with her.
For Liu, it would be his brother. Even though he went with Jane to find him, Liu wouldn't kill Jeff until absolutely necessary