[RKDinOKC]

The saying is...You can lead a horse to water, but you can't make it mow your lawn.

Sounds to me like you might be dumping projects on them too much to quickly.
Start by just having them hand you the tools, clean and put them away, clean the shop.
Explain what you are doing and why.
Start them dong wrenching by taking things apart or off the car.
When you do have them put something back together help them doit, don't assign it as a task.
\