We have one of the Wacky Walkr couplers, but I'm not sure you are asking for a coupler.
Look under products for the crazy couplr. It works much better than other couplers I've tried.
https://wackywalkr.websitesource.net/
Keep in mind that unless your girls walk at close to the same rate they will kind of yank each other around on a coupler, and you may prefer them on their own leads.
This is the style I was thinking you were asking about, but I have no real experience with them:
Adjustable 2 Dog Lead by Timberwolf from Golly Gear