Sorry to disturb you.
1. There are others who has also helped, whom the editor would like to assure that they have not been forgotten.(This sentence comes from my grammar book)

2. There are others who has also helped, that the editor would like to assure that they have not been forgotten.

3. There are others who has also helped, the editor would like to assure them that they have not been forgotten.

Question: Which is/are grammatically correct? (I want to change the "has" into the "have" ??)
From the #3 , I guess:
the "they" and the "them" here both refer to the "others" here, Is my guess correct?

Question

Sorry to disturb you.
1.  There are others who has also helped,  whom the editor would like to assure that they have not been forgotten.(This sentence comes from my grammar book)

2.  There are others who has also helped,  that the editor would like to assure that they have not been forgotten.

3.   There are others who has also helped,   the editor would like to assure them that they have not been forgotten.

Question: Which is/are grammatically correct? (I want to change the "has" into the "have" ??)
From the #3 , I guess: 
the  "they" and the "them" here both refer to the "others" here, Is my guess correct?

Answer

Agree with the others but it would read a lot better as two sentences. There are others who have also helped. The editor would like to assure them that they haven’t been forgotten.

Answer

The editor would like to express his gratitude to all those who have helped. (Perhaps giving details about the type of help)

Answer

Yes, you're correct that "they" and "them" refer to "others." However, there are a few grammatical issues in the sentences. Let's correct them:

1. Corrected: "There are others who have also helped, whom the editor would like to assure that they have not been forgotten."
    * This is grammatically correct after changing "has" to "have."

2. Corrected: "There are others who have also helped, that the editor would like to assure that they have not been forgotten."
    * While "that" can be used informally, "whom" is more appropriate in this context because it refers to people. The sentence would be better with "whom."

3. Corrected: "There are others who have also helped; the editor would like to assure them that they have not been forgotten."
    * This sentence is correct. "Them" refers to "others," and the use of the semicolon is appropriate.

So, all three sentences can be corrected with the appropriate changes.

Answer

### Grammatical Analysis

1. **Sentence 1:** 
   - "There are others who **have** also helped, whom the editor would like to assure that they have not been forgotten."
   - **Correction:** Change "has" to **"have"**.
   - **Note:** This sentence is grammatically correct after the correction, but "whom" could be better replaced with "that" for clarity.

2. **Sentence 2:** 
   - "There are others who **have** also helped, that the editor would like to assure that they have not been forgotten."
   - **Correction:** Change "has" to **"have"**.
   - **Note:** Although grammatically correct, using "that" in this context is less formal than "whom."

3. **Sentence 3:** 
   - "There are others who **have** also helped, the editor would like to assure them that they have not been forgotten."
   - **Correction:** Change "has" to **"have"**.
   - **Note:** This sentence is grammatically correct.

### Clarification on "they" and "them"

- In **Sentence 3**, your guess is **correct**: both **"they"** and **"them"** refer to **"others."**
- "They" is the subject pronoun, while "them" is the object pronoun. In this context, "the editor would like to assure them" is correct because "them" is the object of the assurance.

### Summary

- All sentences need to change **"has"** to **"have."**
- **Sentences 1 and 2** could be improved by replacing "whom" or "that" for clarity.
- **Sentence 3** is the most straightforward and correct option.

If you have any more questions or need further assistance, feel free to ask!

Answer

All three are wrong grammar. You must change "has" into "have, like you suggested.

As for the remainder of the sentence...

Option 1 is better than option 2. The word "whom" is smoother than the word "that", in that particular place - due to the complexity of the sentence, the precision of whom is appreciated there. But option 2 is not strictly wrong, it's just inferior - it's a more awkward, less clear way of saying it (between educated native speakers, at least).

Option 3 would be the clearest way to say it, of all three options, if only we replaced the comma with a dash or a period. As it stands, the grammar is so poor when using a comma there, that we can say option 3 arguably has the worst grammar of them all until this is fixed.

You are correct in guessing that "they" and "them" both refer to "others" in option 3.