When we take our young GSD to visit family he gets overly whiny and excited and begs for petting. I don’t want to offend my family by asking them to ignore him and he also barks a lot in the car when we stop driving, do you have any suggestions?

Being the owner of a working line dog (or any dog , really) means you have to do what is right for the dog. Allowing people to pet him because you don't want to offend someone is doing the dog a disservice. Your job is to do what is right for your dog and even if you want him to socialize with your other family members his behavior is showing you that it's not the right choice for him. At least not right now.

Is he crated in the vehicle? What do you do when he starts barking? Do you only take him to places that he expects high arousal activity like training or play?

I might also correct him right away for the barking in the vehicle because many GSDs love to bark. I'd also take him places and not get him out of the car. I know it's a pain to do but he needs to understand that sometimes he goes somewhere and nothing happens. It's much easier to do this with a crate. My puppies learn from the very first week I have them that they go with me in the car and they randomly come out. (maybe one time out of every 5-7 car rides, always random and sometimes just for a quick pee) Yesterday I went to the Leerburg office with my pup in the car and I never got him out and I was there for 3 hours. Learning how to chill and relax in the vehicle is a very important skill for all dogs but especially if you plan on competing in dog sports where dogs are crated in the vehicle for long periods of time with nothing happening.

Yes, I would tell them to ignore him which means really ignore him. Don't look at him, talk to him or pay any attention to him. I take a crate with me when I visit friends/family and crate the dog somewhere if the people present can't do what's best for my dog.