Jaybay did a great job answering this question from the psychological and behavioral stand point.
Please also have your dog's urine tested to make sure we don't have a urinary tract infection on top of a behavioral issue. If a urinary tract infection is present you can train until doomsday and your dog will not respond.
Training is definitely necessary, but occasionally additional pharmaceutical therapy is necessary, at least at first. Consult with your vet about this.
I'm not a vet, but I've had a lot of training and behavioral experience, so hopefully I can help explain the behavior a bit better. Your dog has absolotely no self-confidence at all. Most people have never had the opportunity to see a normal pack of wolves or domestic dogs and how they interact. Urinating is one way to display submission to a higher more dominant pack member. This behavior is normal. Of course, it is also not acceptable when the dog is living with a pack of humans. :-)
Verbal corrections for any dog behavior generally aren't effective. How many times have you found yourself (or your boyfriend) yelling at one of the dogs about the same issue over and over and over? The behavior never changes. All the dog knows is that their humans are upset, but not the reason why.
Since your 8-month-old pup came from a previous owner who relied on yelling, he learned to communicate his submissiveness in the only way left to him: urination. This pup is completely and totally intimidated and scared. The more he gets yelled at, the harder he tries to "please" and demonstrate that he knows you are the boss. He pees.
All he needs is some confidence. First, no more yelling. One, it doesn't work; two, it only makes the peeing worse. Confidence comes from knowing his place in his pack, and learning about the rest of the wide world outside his territory. I had a dog exactly like this and she just bloomed once we got her out with the other dogs on daily walks.
The "walk" doesn't mean using a 25 foot flex leash and letting the dogs do whatever they want. YOU have to provide guidance and learn to think like a dog. The pack leader always leads the pack, which means you don't let your dogs walk ahead of you. Obedience training will be a huge help to you and your dogs in this regard. A trainer can help you better understand dog behavior so you can understand exactly when and how to correct unwanted behavior.
I think you, your boyfriend and both dogs will see a tremendous improvement if you will dedicate yourselves to a training program. Hiring a behaviorist would be even better, but they tend to be more expensive. Even reading books will help you gain a better understanding of what is happening and how to achieve the behavior you want to see. Any of Cesar Millan's (The Dog Whisperer) books will be eye-opening experience into how dogs think, and would be a great place to start. Just visit your local library. :-)