My son's socks are soaked from his working everyday. I turn them inside out wash them in cold water add fabric softener vinegar detergent and they still come out stiff at the toes. Any suggestions?
If the socks are "soaked from his working everyday", I assume they are soaked in sweat. Sweat contains salt, which crystalizes when it dries, making the socks hard. It can also dissolve chemicals or existing dirt from inside the shoes.
I suggest first washing the socks as you would wash any laundry, then rinsing them thoroughly in a lot of water to remove the salt and any remaining chemicals. To make sure that they're rinsed as best as possible, knead them in fresh water a few times to force everything out that doesn't belong there.
If you have hard water, you can add vinegar to the last rinse, otherwise it isn't really neccessary. You shoudn't add detergent to the rinse, because that detergent itself can make the socks stiff when it dries. If you hang the socks to dry with the toes pointing down, that would explain why only the toes are stiff. Detergent only belongs into the washing water, not into the rinse.
Having a look inside the shoes is also worth a try. Did a lot of dust or dirt collect there? Can you wash the shoes?
With regard to socks, they usually get dirty only with sweat, dust and dead skin cells. Therefore, any normal washing should remove the stiffness. I washed socks manually many times, with good success. I machine-washed socks (as well as other clothes, obviously), no stiffness.
My hunch is that if you use powdered detergent, you use too much, and it remains inside the fabric. Long term, this will lead to health problems, since that detergent will affect the skin on the feet. Use less detergent. Or rinse twice. Even if you use liquid detergent, you might still use too much.
Another potential problem might be the socks themselves. The material might be bad quality, or they might be old, or they might be badly manufactured. If this is the case, just throw them away (at a moment of your choice) and buy better ones.
Before throwing anything away, just buy new socks, different material, different brand. See if the problem persists, or if the problem goes away. Act based on the conclusions.