Double auxiliary modal verbs

English as a Second Language English Vocabulary, Grammar and Idioms
1
  1. You must have to know the password.
  2. A person must have to be president.
  3. He must have to be present.
  4. You must have heard this song.
    Please correct the above.
    If any sentence is wrong, please explain with its grammatical points.
    Thanks.
2

You would need further context to explain why this particular tense were being used rather than a simpler form. 4 is quite common, but the others are not usually required.

3

Your first three sentences are really overstating the sense of necessity. They are an amalgam of ‘must’ and ‘have to’ and in that respect are unacceptable. Your fourth sentence has nothing to do with ‘have to’ expressing necessity but an example of the perfect infinitive after ‘must’. In other words you would say: You must hear now or You must have heard then.

4

Alan, I think the following should be possible and acceptable:

You must know the password or You have to know the password.
He must be present or He has to be present.

However, "A person must (has to) be president’ does not make good sense.