What is the right way to join aluminum house wiring to aluminum fixture wiring?
I guarantee it's not aluminum wire on the fixtures.  I see fixtures with multistrand tinned wire all the time.   

Install AFCI breakers in your panel.  These detect arcing from bad connections, which is the crux of the problem with aluminum.  Killing yourself to replace every Al-Cu splice in the house doesn't make much sense when you can just detect the root problem.  

Then you can use any listed method, such as the generally-regarded-as-poor purple wirenuts, or the excellent Alumiconns.