1. If they had tried their best, they would have succeeded in the interview. (subjunctive mood)

Question

2. As they didn't do their best, they didn't succeed in the interview.
3. As they didn't do their best, they wouldn't succeed in the interview.
4. As they didn't do their best, they couldn't succeed in the interview.

#2, 3 and 4 are in the indicative mood.
What is the same as the Sentence among Sentence 2, Sentence 3, and Sentence 4?

Your indications of subjunctive and indicative moods are correct, as are the tenses.

I don't understand your question, though. "What is the same as the Sentence among Sentence 2, Sentence 3, and Sentence 4?" What is "the Sentence"?

??

There are two things that are identical. The introductory adverb clause is identical. In addition the verb in each of those three sentences is in the indicative mood.

1. If they had tried their best, they would have succeeded in the interview. (subjunctive mood)

2. As they didn't do their best, they didn't succeed in the interview.
3. As they didn't do their best, they wouldn't succeed in the interview.
4. As they didn't do their best, they couldn't succeed in the interview.

#2, 3 and 4 are in the indicative mood.
What is the same as Sentence 1 among Sentence 2, Sentence 3, and Sentence 4?