The words we'll, weal, wheal, wheel sound the same but have different meanings and spellings. Why do we'll, weal, wheal, wheel sound the same even though they are completely different words?
The answer is simple: we'll, weal, wheal, wheel are homophones of the English language.
Contraction of we will.
The welfare of the community; the general good: the public weal.
Prosperity; happiness: in weal and woe.
A ridge on the flesh raised by a blow; a welt.
A small swelling on the skin, as from an insect bite, that usually itches or burns.
A solid disk or a rigid circular ring connected by spokes to a hub, designed to turn around an axle passed through the center.
Something resembling such a disk or ring in appearance or movement or having a wheel as its principal part or characteristic, as:
The steering device on a vehicle.
A potter's wheel.
Definitions from The American Heritage® Dictionary of the English Language, 4th Edition and Wordnik.
Homophones (literally "same sound") are usually defined as words that share the same pronunciation, regardless of how they are spelled.
If they are spelled the same then they are also homographs (and homonyms); if they are spelled differently then they are also heterographs (literally "different writing").