Mila and Yolene at least have a passing interest in collars from their designs, Mila having light one and Yolene having a thick heavy collar that covers her entire neck. Fefe is by nature in her level of human functions is into petplay. Jasper is of course into both dog and cat petplay, but there isn’t a fetish she’s tried at least one time. She’s a kink machine.
Beatrix, despite having a twin cat collar with bells isn’t even familiar with what petplay is. She’s too busy exercising and playing games that she’s very ignorant to mature things like that. Unlike her brother, who steeps himself in reams upon reams of romance and erotica, Beatrix sees her collar part of her outfit rather than something sexual.