My cats are attacking one lone one.

Question
I have a question for you... we have 4 cats ... we had 5 however he was our lone male :( passed away from severe kidney problems that was likely hereditary :(  (I do believe like a rooster he kept the peace among the girls*)  anyways now our girls  2 black are sisters one is the queen bee.
However we have one girl Butters (white), I think it is interesting because she seems to mind her own business* she purposely stays out of the way, and really they all seemed to let her mind her own business.. Lately they have been really bothering her :(
It started off one of the blackie sisters girls.. not the queen but second in command.. just constantly searching her out... ok well she is looking for her place and constantly tries to beat the queen bee* (her sister) but cant* So she picks on her... BUT now 2 others are doing the same thing.. She is starting to coward :( more...
I am getting worried to why they are picking on her.. she doesnt seem to do anything. All they are is chasing her hissing growling and the occasional paw raise .. no one has hurt each other but worried they may... any thoughts to bring peace to this home? Our boy just passed away in the beginning of Janaury, It is tough on us all.. and I know they notice he is gone* his sister especially notices (our last cat grey).   Now this girl who is getting picked on isnt siblings with anyone.. where all the others were seperate but 2 blackie sisters, then the boy and the other girl grey girl were siblings... I would think maybe this... BUT the 2 black sisters dislike each other. Thanks

Answer
Lisa,

The one thing for sure is that we humans really do not understand how cats inter-relate to each other.  Secondly, any human intervention tends to be counter-productive. So, I would leave them be and let them find their own way to deal with each other.

Be careful not to ascribe human motives and emotions to the ways cats inter-relate. As long as no one is drawing blood, I would grit my teeth and ignore the by-play. Once one of the group is gone, they have to realign how they relate to each other, and, as often as not, things take a while to settle down.  However they decide to relate, you are kind of stuck with it.

Best regards... Norm.