Double Notes And Repeated Notes

I have particular difficulty on double notes trill and double note scale. At least for the right hand, I'm actually up to speed for a short Mordent. But I cannot play the two notes at absolutely the same time. At least it's highly inconsistent. Needless to say, it breaks down totally for trill ! Any ways to practice it? Any sections from Alan's 2 books that are particularly relevant? Another problem is repeated notes. Any orthodox way (in the good sense of the term orthodox) to play it?

To get you started, I will point out a relevant section from Alan's book: Chapter 42, The Hidden Problem in Double Notes : . -pages 252-259 in (1st ed). In thirds, we tend to think our "weak" fingers (i.e. 4th and 5th) are the culprits. Alan brings our attention to the fact that, typically, it is the thumb and 2nd finger which are creating the dysfunction. ~ A very general piece of advice: every third you play, regardless of what note you are voicing, you are always balanced toward the thumb. ...Anyway, good luck. Thirds are a bitch. Chopin's op. 25 no. 6 is genuinely the only one that I consider truly horrific.