The short answer is "no - it's a bad idea".
From time to time, people ask if they can buy more than one puppy from us. It's very rare that we say yes.
When you buy a puppy or even a trained sheepdog, it's very important that the new dog 'bonds' with you as quickly as possible. All dogs are pack animals. That means they form a strong bond with the other members of the pack (whether they be dogs or humans).
Whether there are other dogs around or not, the dog should include its owner (and members of the owner's family) as respected pack members, and it's important that the dog sees its new owner as its pack leader.
Establishing yourself as pack leader doesn't mean you need to be cruel to the dog. Far from it. All you need to do is be Firm, Fair and Consistent. Teach the dog good manners. This makes training far easier than it will be if there's no bond
If you buy two puppies together, particularly pups from the same litter, they will already have a very strong bond between themselves and unless you know how to cope with this, their bond could be so strong that it will exclude you!
If you're buying a puppy, it's far better to get one, and establish a good bond with it. Then perhaps after about six months, get another puppy. You'll find that there's no problem with bonding, and in fact, the older dog will teach the younger one quite a lot about daily routine and how you like your dogs to behave.
Whether there are other dogs around or not, the dog should include its owner (and members of the owner's family) as other pack members, and it's important that the dog sees its new owner as its pack leader.