My heart goes out to you, and I, too, have no "sound" advice or explanation. I'll just sympathize with you and mention you and your folks in my prayer.
In my family, I, too, saw examples of terrible, extremely obnoxious behavior of parents toward their children, a behavior that goes against any human possibility of "honoring." My paternal grandfather - essentially a very well-educated, highly respected man, - became very obnoxious and cruel with his son and his daughter-in-law as he grew old. When he was in his late 70-s and 80-s, he would often visit my parents' apartment and stay there very long, interfering with their lives, scolding them, demeaning them (sometimes even calling them indecent names, names that could not even be pronounced aloud in good society or in the presence of children!), and simultaneously begging for money, allegedly as a "loan" (which he, of course, never paid back). He did not really need that money - he was on a state pension and had everything an aged man needs, but it tormented him that his son and daughter-in-law earned what he perceived as big salaries... My mom began to hate him with a deep, almost animal hatred, and to spill this hatred on my dad, which probably was one of the leading factors that lead to his suicide in 1996.
Another awful example was my maternal grandmother, again, an extremely well-educated, highly intellectual, erudite woman who, aparently, did not have a slightest maternal feeling toward my mom. Paradoxically, she was very good to me, but to her daughter she was dominant (obnoxiously dominant), rude, unkind. She was obsessed with the idea that my mom, - her only child who had been born in a very short and loveless marriage to a guy who had been essentially a stranger to my grandma, - was ugly and stupid. When my mom was in her 30-s and 40-s and 50-s, and my grandma in her 50-s and 60-s and 70-s, the two of them could not be in the same room without a terrible fight, which, again, tormented my dad (he would sometimes say that "these two women seem like the next minute they will bite each other's noses off").
My father, however, showed an incredible patience and kindness to his father as well as to his mother-in-law. He would take all their hostilities on himself, serving as a buffer between them and his wife, trying to be diplomatic, to at least try to restore some peace. And, at the terminal stage of his parents' and of his mother-in-law's lives, he took care of them like one takes care of babies. But then, again, when these old folks were gone, a terrible void appeared in his own life, and a terrible fear that he soon would be like they were when they were approaching their end. Yet another contribution to his fatal decision of March 1996...
As for me, I've never really honored my parents. I wish I could be like my dad was with his dad and his mother-in-law, but I never had my dad's heart, his generosity, his kindness and patience. I've been always abrupt, rude, impatient, short-tempered. I know I'll be judged for that.
Again, no particular bright thoughts or sound advice, just commiserating, venting - and praying.