Cat hair loss

My kitties are in need of help!  A year ago my girl cat lost her brother.  We brought in a 7 month old girl kitten.  She hated the kitten at first but now they are buddies.  Eoz the kitten was constantly licking and bathing and losing fur.  Then Zoe, my old cat started doing the same.  We have been to 3 vets.  They have done testing for mites, blood tests etc.  The vet suggested sulfur dips.  Which we started this week.  I am not sure this is the right thing to do since there were no mites in any test.  All the vets ruled out stress.  Although we did try natural remedies and nothing worked.

Zoe, my older kitty is almost bald.  She literally pulls her fur out!  It's very sad.  After this first dip Eoz fur was falling out and she doesn't shed!  

We are at the end of our rope.  Any suggestions?  

Please help our girls !