My understanding is that daughters can be sponsored indefinitely.

However, sons may only be sponsored by family if they are in school (high school or university/trade school) until the age of 25. Otherwise, he will need to find a job and then be sponsored by the company he works for.

He probably can come here and look for a job while under a visitors visa. Don't expect him to find great work though which may be a great motivator for him to go to school.

Grades are a problem, but it may be worthwhile checking out the College of the North Atlantic, Qatar as the have lots of trade programs (and where grades are not paramount).