I urgently need you to check these sentences for me. Thank you very much for all.

1) Mary couldn’t afford to go to the cinema last weekend. She decided to take some money from her brother, Ben (without asking him for it).
2) Her best friend doesn’t know whether or not she should tell Ben about it.
3) I personally think her best friend should talk to Mary and tell her that she must return the money.
Mary should tell her brother what she had (has done).
4) Hopefully he will forgive her.
5) Last weekend my fourteen-year-old friend went to a party and smoked a cigarette.
6) I think I should tell his parents (can I use “inform his parent about it, tell on them, squeak on them,?) though I believe that if I do that, Tom might never speak to me again.
7) I think you should tell them because under-age smoking is against the law in Britain. People under the age of sixteen (under sixteen years old) mustn’t smoke.
8) I also think you ought to (should?) talk to Tom and (to) dissuade him from smoking. You should warn him against the danger of smoking. Maybe you needn’t talk (don’t need to talk) to his parents.
9) I think you should talk to his older brother instead. How about talking to his uncle?

6) any of those depending upon formal or informal language

Everything else OK.

Sra

Sure! Here is a review of the sentences you provided:

1) The sentence is grammatically correct. Mary couldn’t afford to go to the cinema last weekend, so she decided to take some money from her brother, Ben, without asking him for it.

2) The sentence is grammatically correct. Her best friend is unsure whether to tell Ben about what Mary did.

3) The sentence is grammatically correct. The speaker personally believes that her best friend should talk to Mary and tell her that she must return the money. The speaker also suggests that Mary should tell her brother what she has done.

4) The sentence is grammatically correct. The speaker expresses hope that Ben will forgive Mary.

5) The sentence is grammatically correct. Last weekend, the speaker's fourteen-year-old friend went to a party and smoked a cigarette.

6) The sentence can be improved. Instead of using "inform his parents about it", "tell on them", or "squeak on them", a better option would be "tell his parents". The speaker believes that if they inform the friend's parents, Tom might never speak to them again.

7) The sentence is grammatically correct. The speaker believes that the friend should tell Tom's parents because under-age smoking is against the law in Britain. People under the age of sixteen are not allowed to smoke.

8) The sentence is grammatically correct. The speaker suggests that it would be a good idea for them to talk to Tom and discourage him from smoking. They should warn him about the dangers of smoking. They may not need to talk to his parents.

9) The sentence is grammatically correct. The speaker suggests that it might be a good idea to talk to Tom's older brother or even his uncle.

Overall, the sentences are written well, with just minor suggestions for improvement.