PAS by step-mother - Any advice?

[sld02]

We are in the middle of working on a co-parenting plan of our two boys.  We have shared legal/physcial custody.  My ex's girfriend (actually his stepsister- not even married) tries to sabatoge most efforts of co-parenting.  This is REALLY hurting my boys.  (ages 6 & 9)

Anyone with experience on this?  I have been reading everything I can get my hands on.  She is a bit mentally wacko and actually wants to be "Mom".  Do the courts do anything about this when she has legally stepped over the line SEVERAL times by signing documents for both school and doctor as the legal step-parent.  Asked boys to call her that....etc???

HELP!!!