Dave, you have to be kidding!  Invite them for dinner?  We are not told what the parents did to the husband during his childhood.  It may have been unforgivable by any standards.  Let him confront them and support him all the way.  He may need to do this to achieve peace of mind.  The parents sound dreadful just by calling the LW mentally ill.  They sound horrible by any standards and should be avoided.  They are obviously not interested in mending fences.  Depending upon how close your houses are, moving may be the best option.