star trek - Are the people created by Q actually real people or are they just illusions and/or fantasy?

An example of Q 'created people' can be found in (TNG: "Deja Q"):

With no sign of the Calamarain, or the shuttle, the Enterprise crew assumes they are dead, and Picard suggests that they had seen the last of Q. Q, however, appears on the bridge as a horn-player with a mariachi band, making cigars appear in Picard's and Riker's mouths, and materializing around Riker a pair of scantily-clad women to celebrate. Riker denounces Q's scantily-clad females and states that he doesn't want Qs fantasy women.

The question is: Are these 'real' people or just illusions created by Q?

Answer

Whether any given individual manifested by Q is "real" or not is debatable, and probably varies from one instance to another. The Next Generation episode True Q does show that the Q are capable of creating "real" people:

[Q] then reveals that Rogers is a Q, shocking everyone else. When Crusher claims Rogers' birth parents were Human, Q reveals they were members of the Q Continuum who had assumed Human form. They died in an accident and the Q were unsure if Amanda had inherited their powers, but they have begun to manifest so as an "expert in Humanity," Q was sent to oversee them.

This is a lot of effort by Q standards, but it does demonstrate that at least one method for creating "real" people is available to them.

The Mariachis may have been pure illusion. They may have been real people yanked through space and time for the performance. They might have been created whole and on the spot with memories of lives which never happened. Q may have created an alternate universe, bred his Mariachis over the course of billions of local years, yanked them onto The Enterprise for the performance, and discarded the entire setup when he was done.