Whoever's/Whosever's birthday comes first in the year will through a party

Can we say or write 'whoever's or 'whosever'?

Like 'whoever's/whosever's birthday comes first in the year will through a party'.

Whoever's birthday comes first in the year will through throw a party.

@tufguy You've been on the forum for ten years. Am I really expected to believe that you still don't know how to formulate a thread title? Don't ask a question in the title! Use the example sentence you're asking us to look at. We shouldn't have to still be pointing this out. I've changed it for you this time but I'm going to start deleting your threads if they don't follow the standard structure.