Caroline's a vampire herself, so she'll probably want to reach out to him when he's locked himself in his apartment. Maybe get him to feed on bunnies. So he's got an ally in her, most definitely.

Piper ... will probably threaten to blow him up or freeze him continuously if he's a lovely dude. She could try a few spells and potions? But it really depends on how he approaches it/when she comes in as to how she acts. If she becomes aware when he's sending out the emergency message, she'll probably be Nice Piper with the freezing and potions and stuff.