i suppose there would be some antagonism between them to become the no.2 since that is a human tendancy, but it hasnt been highlighted yet in the books.
the most faithful follower has to be a fanatic who would blindly follow whatever the master says. hence Bella must be the one. someone like Lucius is more intelligent than faithful, and such people would think of themselves first before their master, which differentiates him from Bella.
Voldemort would know that. i think he has managed his followers: both the fanatics and the powerhungry one quite well.
i am wondering what Voldy thinks Snape is....