Somebody: As Pronoun
'Somebody' as an indefinite pronoun means an unspecified person.
Somebody: As Noun
'Somebody' as a noun means a famous, renowned person, someone who is a celebrity.
He wants to be a
When Can We Use "Somebodies"?
Only when 'somebody' is used as a noun, it can be used in plural form. Otherwise, when we want to refer to a group of unspecified people, we should use 'some people', NOT 'somebodies' as an indefinite pronoun.
They all think they are
Here, because 'somebody' is a noun, we can use it as a plural noun.
This is the plural form of the sentence 'somebody was shot at the crime scene.'