I left out the following sentences. I really don't know which alternative is best.

1) Influenced by Lord Henry’s words on youth and beauty, he is terrified of aging (ageing?). He fears that he will lose everything when he loses his youth.
2) He impulsively vows that he will when he grows old and wishes that the portrait could (would/might?)grow old (age?) in his place whereas he remains (stays or would stay) young.
3) Dorian’s wish about the painting introduces the Faust theme, which Wilde develops throughout the book. (The Faust legend was well known to Wilde through popular culture.)
4) Faust, legend has it, sold his soul to the devil in exchange for knowledge and power.

Ageing is British English and aging is American English spelling.

2. would grow old / or / would age

The other things in parentheses are also possible in #2.

Sra

To determine the best alternative for each sentence, we can consider the context and meaning of the sentences. Here are some possible options for each sentence:

1) Influenced by Lord Henry’s words on youth and beauty, he is terrified of aging (or ageing?). He fears that he will lose everything when he loses his youth.
Alternative: The choice between "aging" and "ageing" depends on the preferred spelling in your intended audience or region. Both spellings are correct; "aging" is more commonly used in American English, while "ageing" is more commonly used in British English. Choose the one that aligns with your intended audience or the style guide you are following.

2) He impulsively vows that he will when he grows old and wishes that the portrait could (or would/might?) grow old (or age?) in his place, whereas he remains (or stays, or would stay) young.
Alternative:
- "could" implies a hypothetical situation. He wishes that the portrait has the capability to grow old, but he knows it's not possible.
- "would" implies a conditional situation. He wishes that the portrait would grow old if it were possible.
- "might" implies a possibility, giving a sense of uncertainty. He wishes that the portrait might grow old, but he's unsure if it's achievable.
Choose the alternative that fits the intended meaning of the sentence based on the character's desires.

3) Dorian’s wish about the painting introduces the Faust theme, which Wilde develops throughout the book. (The Faust legend was well-known to Wilde through popular culture.)
Alternative: The sentence seems complete and clear. No alternative is necessary.

4) Faust, legend has it, sold his soul to the devil in exchange for knowledge and power.
Alternative: The sentence seems complete and clear. No alternative is necessary.

In conclusion, the best alternatives depend on the specific context and the intended meaning of the sentences. Choose the options that align with your intended audience, style guide, and the overall message you want to convey.