***** NOT A TEACHER *****
I know how you feel: it is confusing.
Many learners make the same mistake.
I believe that the main problem is: the verb "to be" is special. Learners forget this fact.
a. These sentences are correct.
i. To make the question, simply move "are" to the front:
"Are these sentences correct?"
Please remember: "to be" is a special case. It is not treated like other verbs.
According to what I have read, many (many!) years ago, the English people made a question like this:
You eat apples. Eat you apples? (I believe that some languages still use this way to make questions.)
Then the English people (over the years, of course) decided to use "do," "does," or "did" for questions (and the negative).
People use those little words if the verb is not " to be."
Oh! You say that "correct" is a verb. Yes, it is in "The teacher is going to correct the sentences." But in your sentence,
"correct" is an adjective. As you remember, an adjective describes somethiing:
Are these sentences correct, incorrect, interesting, good, offensive?
If you are still confused, please continue to ask until someone is able to explain it in a way that you understand.
HAVE A NICE DAY!