Howdy and welcome to the site.
I have bitches that have been together from birth and are now 2 years old, living in the same kennel with their dam. It can work. Most of my dogs are separated from their dam and littermates. Babs and Jenna were together for 18 months, and they are fine. Neither has been ruined by being in with another dog, and they all think I am better than chopped liver.
I have just one puppy who is 7 months old, who is far more interested in running outside and barking at the others, than being inside with me. So I understand that there are these dogs out there. If I found it to be an issue, (it's not for me), I would separate the dogs -- crate/rotate as they suggested. But I would give them some time each day, something fun we do together, a walk together, and some play time in the yard, then I would separate again. I would take each of the puppies to classes separately and work with each one separately.
I think the idea of having more than one dog, though, is to have dogs that are together. What I would be working on individually is making my interaction more important than dog interaction. So I would be working on stuff that is fun and challenging for the dogs, like agility. Or maybe something that uses their natural instincts like herding or tracking. I want getting in the car with Susie to be more important than a host of dogs running around in the back yard. But I still want the dogs to behave in all situations, so working on agility or herding one day a week, working on obedience, 6 days, maybe 3 10 minute sessions a day.
Start the sessions doing something they will be successful with, so you can praise and treat if you are using treats. You want to start a session on and up-beat. Training time should be fun, it is interaction with you that you are doing. I would work on focus exercises, WATCH or LOOK. This is kind of a game where you want the dog to look at you and make eye contact. Look at your face. You start out by giving him the treat when he turns toward you and looks toward your face, then you wait until he makes eye contact, give this some time with each step. days. You aren't in a hurry. Then put the treat in your hands and hold them out parallel to the ground toward either side. Only give him a treat when he looks at your face and makes eye contact. Keep the session short, and end when he wants more. End each session with something fun that he will be successful with so you can praise him. Tug, is something dogs love, and you can then have a quick tug session.
As you progress you want to start weaning treats, and making him work for them, doing more than one thing successfully, or doing something quickest or the most polished to get the treat. Be liberal on praise with treats, and without treats, but after the weaning from treats, you can make him work for the praise too. You want him to see you as the source of all that is wonderful in the world. And the way to do this is NOT to pump him full of praise and treats continually.
After a good exercise session, a quick romp in the yard with the other dog. OK. Then put him up and work with the girl. Same thing.
Teach them to settle. Do it in training sessions at first. Teach them to down, and to settle. Teach them that in the house they must settle. If they start romping in the house, immediately put both dogs in their place and after a little while let one out. Then put that one away and let the other out. It might take a few days for them to understand that if they are inside, and they start romping, the game stops immediately. I don't like using crates or punishment, but continued play in the house is not going to help matters. They need to learn to settle together. Sure they can learn this after they are 18 months apart from each other. By then they are sexually mature, and still somewhat puppyish, but have much more adult temperament showing. They can learn this sooner, and it won't hurt them. It might be easier if they are well-exercised prior. It may help if a set routine is established. Dogs are creatures of habit, and they will enjoy winding down with you every evening together, if we can get them past the constant play.
Good luck.