Can someone tell me if my sentences are correct, please? I'll be very thankful to you.

•When I arrived at the hotel, someone was cleaning my room
•If I had known that he was so rude, I would have never married him.
•You would tell the truth if you were good friends
•I wouldn’t have answered the phone, if I had known that it was him
•If you don’t water the garden, the plants will die.
•Look! The man who is crossing the road is my granpa.
•He had been driving for two days when he reached his destination at last.
•I won’t be able to go skiing with you because I will be very busy studying next week.
•You have been packing all morning, do you need any help? (it's all morning you have been packing??)
•When I arrived last night, my mother had already come back and was giving dinner to children.
• You shouldn’t eat many fats which are bad for you health.

Here are the corrections and explanations for each sentence:

1. When I arrived at the hotel, someone was cleaning my room.
- This sentence is grammatically correct. It is in the past continuous tense, indicating an ongoing action in the past.

2. If I had known that he was so rude, I would have never married him.
- This sentence is grammatically correct. It is a mixed conditional sentence, expressing a hypothetical situation in the past with an unreal outcome.

3. You would tell the truth if you were good friends.
- This sentence is grammatically correct. It is in the second conditional, expressing a hypothetical situation and its probable outcome.

4. I wouldn't have answered the phone if I had known that it was him.
- This sentence is grammatically correct. It is another mixed conditional sentence, expressing a hypothetical past situation and its unreal outcome.

5. If you don't water the garden, the plants will die.
- This sentence is grammatically correct. It is in the first conditional, expressing a possible future outcome based on a condition.

6. Look! The man who is crossing the road is my grandpa.
- This sentence is grammatically correct. It uses present continuous tense to describe an action happening at the moment of speaking.

7. He had been driving for two days when he reached his destination at last.
- This sentence is grammatically correct. It uses past perfect continuous tense to describe an ongoing action that started in the past and continued up until another specified time in the past.

8. I won't be able to go skiing with you because I will be very busy studying next week.
- This sentence is grammatically correct. It uses future tenses to express an inability to go skiing in the future due to being busy studying.

9. You have been packing all morning. Do you need any help?
- This sentence is grammatically correct. It uses present perfect continuous tense to describe an action that started in the past and is still ongoing at the present moment.

10. When I arrived last night, my mother had already come back and was giving dinner to the children.
- This sentence is grammatically correct. It uses past perfect tense to indicate that the action of the mother coming back had already occurred before another past action (arriving last night) and was still ongoing at that time.

11. You shouldn't eat too many fats which are bad for your health.
- This sentence is grammatically correct. It should be "your" instead of "you." It uses modal verb "shouldn't" to express advice or prohibition, and "fats" should be plural since it refers to a general category of food.