Is it true that according to freud when several people objects or events are combined into a single dream image the dream process of secondary elaboration has taken place?

No. Secondary elaboration refers to adding to the details of the manifest dream, that is "elaborating" on that dream when awake and remembering the dream. The dreamer's conscious mind might attempt to fill in the gaps of the remembered dream, or add subtle interpretations that were not evident in the actual dream. For example, when remembering a dream of an older man in a uniform sitting on a sidewalk, the dreamer might describe "a homeless veteran." That is secondary elaboration.

Freud believed that secondary elaboration could distort or disguise the true latent meaning of the dream.