I still have a few doubts on the use of the word "narrator". Shall I refer to it as "it" or "he".

1)For example: "The narrator can be obtrusive, when he/it interferes in the narration giving his/its own points of view.
2)I added a few other sentences I'm doubtful about.
The film director (OR: Film director?) Stanley Kubrik offered (is "gave" possible) him the role of...
He acted/appeared/was (but not: did) in many films.
3) All (of) your questions lack either the subject or the auxiliary. Remember you can't ask any questions without including a subject.
4)He and his family moved to London. (better: he moved with his family to London).
5) Re-write all your questions correctly at least 5 times.
6) If I were (was is possible?) invited to a party, I would wear the new red dress my mum gave me for Christmas (or as a Christmas present).
7) What did you get from your mum for Christmas? What did your mother give you as a Christmas present?
(What is the best way of asking what I someone received for Christmas?)
8) On Epipany I stayed at home since I had a bad cold and a temperature. I made some buscuits and I filled the Christmas (?) stocking with them. Then 9) I hid it under my son's bed. On epiphany morning my child woke up and went in search of his stocking full of biscuits. (Can you also say: looked for his stocking?)
10)In Spain it is tradition to fill the stocking with every kind of sweets and let the children find it on Epiphany morning. Bad children receive only sweet coal (I don't know the name of it in English: it looks like a piece of coal but it is sweet and it can be red or black).

He/she not it.

2. film, either offered or gave. either actted or appeared

3. use of
4.& 5. what you have is fine.
6. were is correct
7. either
8. spelling errors
9. yes, either are correct
10.correct.

I use "s/he" when gender is not determined. It's a little shorter.

1) The use of "he" or "it" to refer to a narrator depends on the context and the individual preferences of the author. In general, when referring to a narrator, it is common to use the pronoun "he" or "she" if the narrator has a specific gender or if the narrator's voice is intended to be personal or subjective. On the other hand, the pronoun "it" can be used when the narrator is more objective or detached, such as in the case of an omniscient narrator. However, there are no strict rules and it ultimately depends on the author's choice.

2) Both "film director" and "the film director" are acceptable phrasings. It depends on whether you are referring to a specific film director (using "the") or a general role (using no article). Regarding the verb, "offered" is more commonly used in this context than "gave".
As for the second sentence, all three options ("acted," "appeared," and "was") are grammatically correct, but the choice depends on the specific context and intended meaning.

3) The correct sentence should be: "All of your questions lack either the subject or the auxiliary." Both "all" and "of" are required in this sentence.

4) Both sentences are grammatically correct, but your suggestion of "he moved with his family to London" provides more clarity about who moved.

5) Re-writing a question multiple times is a useful practice to reinforce grammar and sentence structure. The sentence itself is grammatically correct.

6) Both "were" and "was" are acceptable in this context. However, "were" is more commonly used in formal writing, while "was" is commonly used in informal or spoken English. Therefore, "If I were invited to a party..." is typically the preferred choice.

7) Both "What did you get from your mum for Christmas?" and "What did your mother give you as a Christmas present?" are appropriate ways of asking what someone received for Christmas. The choice between "mum" and "mother" depends on the familiarity and relationship with the person being asked.

8) The sentence "On Epiphany morning my child woke up and looked for his stocking..." is grammatically correct. "Went in search of" is also acceptable, but "looked for" is more commonly used in this context.

9) The sentence "Then I hid it under my son's bed." is grammatically correct. The use of "looked for" (as mentioned in the previous answer) is also a suitable option.

10) The term for the sweet coal you describe is "sugar coal" or "sugar candy coal." It is a common confectionery item associated with Christmas and Epiphany traditions in various cultures.