I would put the younger dog on a harness, then add in a prong with that as more control is needed-running two lines.
Using a harness gives the handler less control, as the dog pulls. But barking can be restricted if you just use a collar, so many people use the harness to help the dog, not so much the handler.
You could put the dog on a post if you can't hold him, but that takes skill as well, to keep the line from tangling. Or have someone hold the line while you are near your dog, so you are essentially supporting your dog with your presence, but someone else is handling the line(s).
There is also the thought that the dog should work independently, so the handlers presence isn't needed. When I did a workshop with a well known helper, he wanted the dog between the handlers legs to show the teamwork/dog needed to know he had his partner constantly. Different methods....both seem legitimate in the big picture.
Really, I've seldom used my agitation collar more than a few times.
This harness is really nice for young dogs, and very well made for the price. Even though it is a 'tracking' harness, many use it for protection work, not tracking. https://www.bridgeportequipment.com/...x?productId=96