I learned how to lead two horses at a time by leading pairs of broodmares from the barn up a hill for a long time to their paddock. On occasion, some pairs wanted to part company. When two 1200 pound horses wanted to go somewhere without you, I had to devise a way for them to fight themselves. I did not want to chase loose horses.
My solution was to hold the leads, as you see in the video. The horses could pull against each other all day, but all I needed to do was grip the two parallel leads with my one hand. This technique works well unless they both want to pull in the same direction. In that case, they will win, but it never seems to happen. They usually pick different directions, so my success rate was 100%.
Images, if any, for this topic are in a gallery located at the bottom of this page.
The audio isn’t great here, but the concept is evident. You can also use one hand. But now, you are no longer the weakest link. However, I have had rotten halters break, so be careful (and use good equipment).