Seems unbothered by anything his darling does, but the moment they’re in danger he’s the most protective yandere out there. Sans is the most likely to kidnap his darling, though he thinks about it often he only does it once he sees them in some serious danger. He’s pretty lazy, so it takes the extreme for him to really try and kidnap his darling. He, unlike most yandere's, doesn't think he has to keep his darling away from the world. That would be selfish, wouldn't it? It really takes something horrible for him to do it.
I seriously think he wouldn't do it. Papyrus is incredibly good at hiding his possessive tendencies, so it's likely that he and his darling are in a normal and loving relationship. He would rather keep it that way too. To a degree, I can see him convincing his darling to stay isolated with him for several weeks on end, but it isn't outright kidnapping. Basically, he's very manipulative. His darlings happiness matters to him of course, but keeping them to himself seems to matter just a little bit more.
She does it, but no one notices. To them, it just looks like she's in a very close-knit relationship with her darling. Unlike Papyrus, Toriel’s darling is very aware that they are being forced to stay with her, however, they can't really do anything about it. If they try to ask for help, no one will believe them. Toriel is just the sweet Goat Mom who wouldn't hurt a fly! Being blunt, her darling is stuck with no one to help them, and Toriel knows that. He doesn't want her darling to hate her, so she does extra nice things for them. She's a sweetheart... When she's not threatening them to stay with her.
{this is my first post, but feel free to send in requests!}
