Siblings can be difficult, especially school age ones. I stopped doing before and after care, as I found I was constantly dealing with behaviour issues. It was too difficult to deal with their behaviour and try to supervise the infants and toddlers.
I’m not sure if you do outdoor time after school, but that’s what we did. The kids got picked up from school, we came home and had snack as a group, and then straight outside until closing time.
It sounds like they need really strong boundaries set by you. Try setting firm limits for a month, and if no improvement then get rid of them. My guess is this behaviour is acceptable at home, so why wouldn’t they do it elsewhere? You might be fighting a losing battle if the parents aren’t on the same page as far as limits and behaviour goes.