I recently acquired a pair of cockers who are about 2 months old now. They are bro and sister and were very cute and loving together so we decided to not separate them.
Since then, I've heard people tell me that it's not a good idea as it's harder to train 2 together. I've noticed that now they are starting to fight more than they play together and toilet training them is much harder then my previous experience with another cocker as they seem to distract each other.
We have since separated them in different enclosures but ultimately we want them to have the freedom of our house together.
I have also heard that they may be too attached with each other and not bond with the owners.