Brad Maddox tweeted the following:

As GM of Raw, the #SummerSlam Axxess match is officially made. @NatbyNature & @mariamenounos vs. @NicoleandBri & ???. Find a partner, Brie!

As of Monday, Nikki Bella wasn't cleared to return and they had planned to do a single match between Natalya and Brie Bella due to this. That still appears to be happening at the pay-per-view. The celebrity tag-team match will take place at AXXESS. More shortly.