How many humans can fit inside the sun?

Many more than all the humans on earth.

If the average human has a body volume of 3 cubic feet (3 cubic foot = 0.084950539776 cubic meters). And the Sun's volume is 1.409 x 1018 1409000000000000000 Cubic kilometers (1 cubic kilometer = 1000000000 cubic meters) which means the volume of the Sun is 1409000000000000000000000000 cubic meters.

Therefore 1409000000000000000000000000/0.084950539776 people could fit into the Sun.