Balls are generally not social animals - they don't particularly enjoy the presence of other snakes - with that being said - plenty of people do raise pairs together some with success and some fail. I don't see any problems with raising up a pair togther - however - would not recommend housing two adults (that have been raised separately) together.
In order to provide proper housing for a pair you basically need to provide enough space for them not to have to be together as well as the opportunity for them to be together if they want. Separate hides on both the hot and cool sides - two water bowls and they need to be fed in a separate container (never inside the cage). Eliminating competition is key to reducing their stress level.
If you are going to do it - keep a close watch on them for signs of stress - like changes in their eating or temperment. Stress can lead to illness which will quickly be passed onto the next one. Be prepared to separate them if need be.
Good luck with them!
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Tosha 
"One of these days i am going to wake up..look around...and realize my place looks more like "Ace Venturas"s than my own." Coldthumb
7.33.0 Ball Python (Harry and Fluffy and gang)
1.0.0 Angolan Python (Skywalker)
0.0.1 Green Tree Python
0.2.0 Feline (Pippen and Pandora)
0.0.1 Dessert Tortoise (Pope John Paul "JP"
2.2.1 Fish (1,2,3,4)
0.0.2 frogs rescued from pool skimmer
0.0.1 lizard rescued from vicious feline