OH Kelly!!
I am so sorry you are dealing with this.
I am no expert in kitty behaivor so I am no help whatso ever there but do offer my support. {{hugs}}
Would Livvy do better in as a single cat home or with less kitties?
I know rehoming her, Sampson or Phoebe would be like cutting of your leg or arm (maybe that would be easier!!) but is she getting stressed from the other cats?
It's ok to vent!!! Advice can come from those who have multiple kitties which leaves me out!!!
PM if you need to talk!