I bought netting to put on my windows to keep my cats in the house - I got it online from a pet store.
Cats are bullies and as your two are kittens they are unable to fend for themselves. Water and noise are the best deterrents.
As you have realised - getting angry and annoyed at a cat doesn't bother the cat one bit. Speak you your neighbour, they may be totally oblivious to the fact that their cat is a thug. Maybe, if it is still an entire male, they can get it de-balled - it helps a bit with behavioural problems.
Cats seem to have a way of winding us mere humans up. It is the smug look on their face which says "and what are you going to do about it?"
Good luck with the thug and, also, your kittens.