Autism: So you have three grandsons that think for themselves, and are not easily influenced by others. Congratulations!
Keep them in sports, regardless of their ability, and in any environment where they are regularly around groups of kids and/or adults. Individual sports to start with, with group coaching is best I found as they can progress at their own rate without feeling like they are 'letting down the team'. They will slowly learn to behave like others through exposure, which is not always a good thing.
...My son was diagnosed as well. It's inherited. My wife is quick to point out it comes from me. I'm also quick to point out most pinball fans have elements of it!
What is the difference between a great sports person and a great scientist/engineer: Their Autism 'interest focus' is on different skills.