The source says the relationship between the three girls and Demi has reached "breaking point" after a series of fights and they have cut off all contact with her.
"Rumer, Scout and Tallulah just don't want to deal with the drama at the moment," a source close to the family tells RadarOnline.com. "Since breaking up with Ashton, Demi has been a mess. The girls were there for her through it all -- the split and the rehab but now they just feel like they need a little distance.
"Demi is just being very needy right now and the girls are tired of it, they want a mother not another little sister. They are all concerned that she is going to relapse and head back to rehab and they can't deal with the stress and worry of it.
"The breaking point was Tallulah's graduation. None of the girls wanted Demi there but she turned up anyway and it was really strained. They had a huge fight afterwards and the girls decided it would be in their best interests to take a break from Demi for a while.
"Another huge bone of contention has been the girls' relationship with Ashton. They all adore him and talk to him regularly which Demi hates, but he was a huge part of their lives when they were growing up and they don't want to break off all contact with him.
"This won’t be forever, but for now the girls just need a little breathing space and to concentrate on themselves and their own lives."
Meanwhile, as RadarOnline.com exclusively reported, the youngest of the girls, Tallulah, is currently embroiled in a nude photo scandal.
A series of photos, purportedly of the 18-year-old topless and smoking a joint are being shopped around media outlets.