Petstores often do things that aren't in the best interest of their animals. Petstores are in the biz for the money, not for the love of herps, so don't do what petstores do if you want a happy, healthy snake!
You *can* keep them together, yes, but it is always better to keep them in seperate cages. This reduces stress, makes cleaning/feeding easier, makes monitoring health easier etc.
If you DO keep them together, make sure the cage is plenty big, with several hides and a good temperature range.