Hey there,
We have 2 sibling GSM 16mo old, I started out walking them together with a halter between the two on my left side. The halter has a ring in the mid. 2 snap hooks one at each end, with their choke chains, it allows them ab 10″ in-between the shoulders. I shorten the leash when needed in heal position. Now days they mind well with out the halter on separate leashes. They both walk on the left side in a loose heal or a tight one at my hip, the close heal is a wee bit more demanding of the two, for lead position.
Regards, Goose & Maverick.