Let me preface by saying that I am a first time dog owner, and my boy is only 5 months old. So I'm far from an expert. But I thought I'd chime in - maybe some of the more experienced members of this forum will have different advice, and I'd defer to their judgment
I'd think that with either of these dogs, at 7 and 10 weeks old, you would need to keep in mind that they are babies. With the 7 week old pup, I'm surprised that he's even been removed from his litter. So, worrying about treating too much, or taking extended walks, I would think, would be somewhat misguided. You don't want to have to constantly treat your adult dog to get him to walk, but I don't think that that is something that's going to happen with a Boxer, and for a little puppy, treating probably isn't bad, and will probably make him *love* walks. For the length of walks, I've heard 5 minutes per month up to a certain age, when they are puppies. I'm not sure what the threshold is, but exercising the dog too hard at that young of an age can be damaging. At 7 or 10 weeks, I'd think that the most important thing would just be getting them used to the leash, and making your trips outside positive. I would assume at that age, you'd be housebreaking too, so maybe them used to going in a certain spot (and associating a command word with them going) might be good ideas.
One thing you might try to acclimate your dog to the leash is to just leave it on (with supervision). Let the dog just drag it around, and get used to it being on.
With my dog, there were times he just didn't want to walk, and times he wanted to pull away, and was hacking from the pressure of his collar on his throat. So I switched to a harness, and, while trying to keep the walks positive, also didn't let him just sit down and end the walk. I also tried to not move forward while there was pressure on the leash (from the dog pulling). The harness isn't a long term solution, as I believe it almost encourages the dog to pull, but for a puppy who really doesn't know well enough to stop pulling forward even if it's hurting him, it's a good way to keep him tethered to you (it also helps when, as your puppy is getting into puppy misdeeds, he has a handle on his back

) When Kevin (my dog) got to be a bit older, I tried walking him with just the collar, and he did much better than he had when he was a real baby.
Hopefully someone with more experience will chime in, but I'd say the problems you guys have can be chalked up to having puppies. They're still trying to figure out what's going on in this crazy world, so of course they're confused by being asked to walk around while connected to a rope held by their giant parents. Don't let the puppies run things (I would think it would be a bad idea to let the puppy get the idea that if he plants, the walk is over), but work on getting the puppy acclimated to everything, keep it positive, and be patient with your baby. They'll figure it out. Soon, you'll have to deal with them pretending like they *need* to go out, when really they just want a walk.