Q: Mark tackled the quarterback, but he managed to complete the pass.
Who he is?
A: the quarterback

Q: The kids asked their neighbors if they had any candy on Halloween.
Who they is?
A: their neighbors

Q: Santa Claus and his elves distributed millions of presents worldwide to the children of the world, but they do not all believe in them being able to give presents worldwide in a night.
Who they is?
A:
the children of the world