Before you get ready to show make sure your horses are prepared for the show atmosphere: a lot of horses, an unfamiliar place, and unless you plan to show ALL of your horses at the same show and stable them together, they need to be comfortable with none of their buddies with them. That means desensitizing them to new situations, and teaching them that they don't need anybody but you to make them feel safe.
The latter is done by making the horse-human relationship good, with you taking a proper leadership role through teaching them ground manners. That's crucial for the youngsters, but also for the older horse: they need to know that you can protect them from anything, they can rely on you for that.
The former is just a matter of putting mileage on them. Take them to places that are new, like small schooling shows, other barns, even trail rides for the older horse and trail leads for the youngsters.
Getting them ready for the show environment will take some time. As far as what judges are looking for, I do not own QHs but two WBs and a Lusitano, so I can't help you there.
Of course, they need to be good at trailering, and have impeccable ground manners. The partnership with your horses will improve as you work on their ground manners, so you will be fulfilling two important factors at the same time.
Good luck and have fun.