Well one is Sistermon Noir and the other Sistermon Blanc, Both of them take care of Hackmon soon to be a Royal Knight. What is lame is that they censored Sistermon Noir for the American version of Hackers Memories.
If you see the link you will see there is not Renamon in the script , the poster is just promotional.
I think they censored Sistermon Noir cause there will be children playing the game.
I think she forgot to add Renamon. It doesn't make sense for all the digimons to be in the cast except Renamon.