I had a similar problem and seem to have it under control now, just a couple weeks after watching a particular episode of Dog Whisperer. But I should point out that my problem was the dogs would walk in front of me, pull me around too much, go in different directions, and get twisted up in the leashes. I don't know if that's the same as your situation as you refer to your dogs as being "laggers" and "draggers". So I'm not sure if it's going to help you any but here's what I did:
I got two Halti collars. I could get the Mastiff to wear the Halti and, after a while, walk with it. I could not get the Rott to keep the Halti on though. His neck is too big and nose too short to get the Halti to fit properly and he'd just paw it off. Seems to be the same as what you've experienced thus far.
I got leads that have handles just a few inches from the collar. So I'm not constantly wrapping and unwrapping long leashes. The retractable leashes I saw didn't handle the weight of the dogs so I couldn't use those.
Once the Mastiff got somewhat used to the Halti collar, I put him on one side of me, the Rott on the other side, held onto the short handles on the leads, kept my arms back & straight, and just walked. The leads are short enough that the dogs are not monkeying around with each other or getting tied up. I simply walk straight, going where I want to go. I don't let them stop to smell trees or go where *they* want to go. If they try to pull, I give the "ch" sound and give the leash a short tug.
Way back when the Rott was a pup we formally trained him using a training collar (choke collar with dull points that would pinch his neck). That worked fine when we only had to really focus on walking one dog (a two year old could walk the greyhound we had). Even though the Rott won't wear the Halti and I'm not using the training collar, he's not nearly as difficult to walk as he used to be since the Mastiff pup is now under control and is back in the swing of things.
Do you have someone (BlueJay?) that can walk one dog while you walk the other dog to start with? I've seen on Dog Whisperer where they started having different people walk each dog until the dogs were in the "right state of mind" and walking calmly. Then, the owner would take both leashes (one dog on each side) and, without breaking the pace, continue walking with both dogs.
One more thing to mention - Cesar Milan sometimes uses a cone shaped collar that I'd never seen before. It looks like he'll be selling those collars from his website. I don't know if they're any good, how they work, or how they compare to the Halti but thought it was worth mentioning.