Can I say,
The owner of the car and the policemen thanked me because of help / helping them (the police) to arrest the thieves.
My parents were pround of me.
(b) The policemen praised John of his quick thinking brain.
Because of helping.
I wouldn't use "because of". Say "for". The policeman thanked him for helping....
HOa bout (b)? Is that correct?
I wouldn't say quick thinking brain. I would say "quick solutions" or for his "being quick".
By the wat don't forget this: praise someone for something.
The policeman praised him for his being quick.