The term "many person" does not have a specific etymology because it is not a common word or phrase in English. However, analyzing the separate words can provide some insight into their origins.
"Many" is an Old English word that can be traced back to the Germanic language family, where it stems from the Proto-Germanic word "managaz". It has a similar meaning in multiple languages, referring to a large amount or quantity.
"Person" has a Latin origin. It derives from the Latin word "persona", which initially referred to a theatrical mask worn by actors in ancient Rome. Over time, it evolved to signify an individual, particularly one's identity or role.
Combining "many" and "person" together, it seems as if "many person" might be intended to convey a large number of individuals.