Priority boarding shouldn't be an issue, I'm *G and was travelling with my (at the time, not yet *G) mother recently. I just walked up with her, showed our passes together and said we were travelling together - no problems.

As for priority security, I don't know which airline you're flying, but vroom is right that it's not an official *G perk. That said, UA does give priority security to any airline's *G and *S flyers, not just their own, so you may be in luck if you're flying UA. However, occasionally I've experienced the priority line being longer than the normal one..!