You only need one, that's all we had since DS7 is homeschooled and we just don't have many people who are in a position to see him in action. I think the chess mentor would be perfect! The application said it couldn't be family, though I'm not sure how far out on the tree they mean, so a grandparent might be ok. We used a family friend who has kids who are GT, I was really grateful she was willing to write it for us because we had no one else we could ask if she wasn't able!