Every vet will have their own charges, and you want to get it done by a proper farm vet - someone you trust. I don't know if they do billies under general anaesthetic or just local, but be prepared for him to be out of it for a while...
Is he horned? and how old are the grandkids?
I would NEVER trust an adult male (sheep or goat) with children, especially as he is not being castrated as a very young kid - he will have testosterone cycling for a while and his behaviour is not certain to become calmer anytime soon...
I simply would not do this.