Consider the following sentence:
(1) The project will include Alice, Bob, and an expected two new hires.
This sounds correct to me; it means we are expecting to hire two new people and will put them on the project together with Alice and Bob. But logically, it seems bizarre to have a singular article "an" together with a number "two"; in most cases a noun quantified by a number word doesn't also get an article:
(2) The project will include Alice, Bob, and two people from marketing.
But removing the "an" from sentence (1) sounds definitely wrong to me:
(3*) The project will include Alice, Bob, and expected two new hires.
Although it could be fixed by inverting the word order:
(4) The project will include Alice, Bob, and two expected new hires.
What is the rule that makes (1) grammatical?