I'm not so sure I understand this answer but I'll try my best. Training a dog to go to the restroom is fairly simple and does not require another dog. If you have two dogs that aren't potty trained then that's all you have, two untrained dogs. Train your dog the simple traditional way. Take the pup out every half hour or hour and give it a command. I have always used "go potty" and once my dogs go, I praise them and give them a treat. I crate trained my dogs as soon as I brought them home. My oldest dog did not play a role in potty training my others (and honestly, we were hoping what you are, that it would make it easier). Don't rely on another dog, just try being consistent with your pup. If that doesn't work, maybe introduce a clicker. Put your dog on a schedule too, they tend do to better in a structured environment. Good luck
The smell from old pee and poop is what draws the dog back to a place to go to the bathroom, so leaving at least one pile of dog doo doo will help your dog go outside. Also, try and create a bathroom routine so the dog knows to go outside. With my puppy, we put a bell on a string hanging from the doorknob. Every hour when we took him outside, we rang the doorbell and only let him back inside after he went potty. After a few days of consistency, he scratched at the bell to be let outside when he needed to go the bathroom, and barely ever had any accidents after that. I hope this helps! Good luck!
No offense, but it sounds like a good reason to get more than one dog. Joking aside, If a dog smells its own poo outside, it will mark the area again. The pee part from another dog is why male dogs cover the old one up. Female dogs tend to do it when they find the right spot.