Like "Are they from delhi" why don't we use "Are they speak English" instead of "Do they speak English"

In first sentence, 'are' is used as a verb because there are no other verbs. In second sentence, there is already a verb, so we used 'do' as an auxiliary verb. If a verb is already in the sentence with its 1st form, we don't use 'are'. If a verb comes with 4th form (-ing),we can use 'are'. Like--- Are they speaking English ? If a verb comes with its 5th (s/es) form, We use does and change the 5th form to its 1st form. Like--- Does he like to cook food?

Tricky Question.

If a question which comes yes/No as answer those questions start with Am, is, are,do,does 1)Here questions without "verb" starts with am, is, are 2) questions with "verb" in 2nd sentence "Speak" is a verb so in this case we form interrogative sentence as "Do they speak English? "