"Expertise" is a singular noun. If there are several people, each of whom has different expertise, you can say "These people have different areas of expertise." If one individual has expertise in many disciplines, you can say "She has many areas of expertise." I'd say areas of expertise as well.
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The meaning of EVERYONE is every person : everybody. How to use everyone in a sentence.
(Definition of everyone from the Cambridge Advanced Learner's Dictionary & Thesaurus © Cambridge University Press)
There is no difference in meaning between everyone and everybody, but everyone is more common in written English, and everybody is more common in spoken English.
You use everyone to refer to all people. Everyone feels like a failure at times. Everyone needs some free time for rest and relaxation.
However, similar to what occurs with collective or group nouns like crowd or team, sometimes a plural pronoun refers back to everyone which is also reflected in verb conjugations: Everyone was laughing at first, but then they all stopped.
Care should be taken to distinguish between everyone as a single word and every one as two words, the latter form correctly being used to refer to each individual person or thing in a particular group: every one of them is wrong