Lavvalast you have done everything you can. I think taking your DILS needs into account is right and kind and not atall disloyal. She appears to be in an abusive relationship and therefore may feel unable to just deal with this issue because of the resulting abuse from her partner. I know how hard this must be as her partner is your son, but his abusive behaviour towards you as well suggests she is having a nightmare time . She is lucky to have a caring MIL! You are right to put the ball in their court and right to provide support, where you can, for your DIL.
Scottish political mess. Is Devolution working?