Sure, here are the corrections and explanations for each sentence:

1. **People say Maths are one of the most popular subjects at school.**
- Correction: "Maths" should be "Math" or "Mathematics" and "are" should be "is".
- Corrected Sentence: People say Math is one of the most popular subjects at school.
- Explanation: "Math" or "Mathematics" is considered a singular subject, so it should be followed by "is".

2. **He has a little free time. He hardly ever even manages to call his mother!**
- Correction: No mistake.
- Corrected Sentence: He has a little free time. He hardly ever even manages to call his mother!
- Explanation: The sentence is correct as it is.

3. **I have few good friends. I'm not lonely.**
- Correction: "few" should be "a few".
- Corrected Sentence: I have a few good friends. I'm not lonely.
- Explanation: "a few" means some, which fits the context of not being lonely.

4. **There were a great deal of flowers in the garden last summer.**
- Correction: "a great deal of" should be "a great number of".
- Corrected Sentence: There were a great number of flowers in the garden last summer.
- Explanation: "a great deal of" is used with uncountable nouns, while "a great number of" is used with countable nouns like "flowers".

5. **All the books on the top shelf belongs to me.**
- Correction: "belongs" should be "belong".
- Corrected Sentence: All the books on the top shelf belong to me.
- Explanation: The subject "books" is plural, so the verb should be "belong".

6. **There usually are two or more bathrooms in each household now.**
- Correction: No mistake.
- Corrected Sentence: There usually are two or more bathrooms in each household now.
- Explanation: The sentence is correct as it is.

7. **A great deal of money are spent on the books.**
- Correction: "are" should be "is".
- Corrected Sentence: A great deal of money is spent on the books.
- Explanation: "money" is an uncountable noun and should be followed by "is".

8. **A few of the audiences is enjoying every minute of the performance.**
- Correction: "audiences" should be "audience" and "is" should be "are".
- Corrected Sentence: A few of the audience are enjoying every minute of the performance.
- Explanation: "audience" is a collective noun and should be treated as singular, but "a few of" makes it plural, so "are" is correct.

9. **There aren’t any sheeps grazing on the lush green pastures.**
- Correction: "sheeps" should be "sheep".
- Corrected Sentence: There aren’t any sheep grazing on the lush green pastures.
- Explanation: "sheep" is both the singular and plural form.

10. **They are sending some man to fix the roof after the severe storm.**
- Correction: "some man" should be "someone" or "a man".
- Corrected Sentence: They are sending someone to fix the roof after the severe storm.
- Explanation: "some man" is incorrect; "someone" or "a man" is the correct form.

11. **The police wanted to interview two men for the robbery last week.**
- Correction: No mistake.
- Corrected Sentence: The police wanted to interview two men for the robbery last week.
- Explanation: The sentence is correct as it is.

12. **Fortunately, the news aren’t as bad as we expected.**
- Correction: "aren’t" should be "isn't".
- Corrected Sentence: Fortunately, the news isn't as bad as we expected.
- Explanation: "news" is an uncountable noun and should be followed by "isn't".