Whoever’s is the possessive form of Whoever. It is also a contraction of “Whoever is”. Whoevers’ may be the plural possessive form of Whoevers but it is not common or necessary in English.
Whoevers is not common in English. The correct form you are probably looking for is “Whoever’s”
Whoever’s is used as the possessive form of Whoever. We use the possessive form of Whoever when we want to show that we are talking about an object that a person we don’t know owns.
Whoever’s coat this is, can they please come here and get it?
Whoever’s phone this is should collect it immediately?
Whoever’s can also be used as a contraction of “whoever is”.
Whoever’s making that noise could they please stop.
Whoever’s playing the trumpet in that song is amazing.
Whosoever can also be used as the possessive form of whoever but it is becoming less popular over time.
Whosoever coat this is, can they please come here and get it?
Whoevers’ is not common in written English and I can’t really think of a context where it could be used.
Who’s ever or Whosoever or Whoever’s?
“Who’s ever” is possible when it is a contraction of “who has ever” or “who is ever”.
I can’t think of anyone I know who’s ever been to Iran.
Whosoever or Whoever’s are both possible forms of the possessive form of Whoever.
Whoever’s idea it was
“Whoever’s idea it was” is a noun phrase in English.
Whoever’s idea it was is a genius
Whosoever or Whose ever?
Whosoever is correct and Whose ever is incorrect.