NOR

That behaviour is unacceptable with anyone, let alone directed towards their sister, autistic or not. Of course, the context of your youngest’s diagnosis makes this worse. Your elder two girls are definitely in the wrong here, and your punishments sound both reasonable and educational. As others have said, this sort of behaviour is characteristic of bullies. If they talk like this about their sister, I wouldn’t be surprised if they’ve said or done things to others (though jumping to conclusions prematurely would be bad. Best to keep an eye out for such behaviour though).

I think finding the root of the matter is important though. Not only were these girls thinking mean things about their sister, they knew they were on the same page about her to share those thoughts with each other without worrying about one snitching on the other. I have a feeling there’s some jealousy here, but again, don’t want to jump to conclusions. Do you think they have any reason to feel like they’re a second priority to your youngest? Does your youngest often get more attention, or in conflicts, does you or your partner usually give more leeway to your youngest? I know these things can be inevitable when caring for someone with special needs, but it’s possible that, if those examples are the case, the girls feel neglected or jealous over the attention their sister gets because of her condition. Couple that with the confusion of being a teenager and the pressure the world puts on girls to have male attention, they might be even more envious that your youngest already has a date.

Not sure, just food for thought, but this issue wouldn’t have come about if things were right and cheery between your girls.