Sounds like you need a brace lead. It's for walking two dogs together. I'm having one made for my two. I have to have a special one made the size difference be tween a Newf and a springer is a problem.
You hook it on the collars then you hook the leash to it . one leash and the dogs can't move around each other. I have the better trained (Merlin) on the outside so I can correct the other(lady) . Works great. I can control both and not get tripped up. You might look in to one.