During these visits, my dad was sometimes there as he was driving back and forth from SE IA to Des Moines because of work. We were never very close. Due to his alcoholism and drug use from my early years, he just wasn't what a dad could have been. I see so much of him in myself now and how it relates to my actions and compassion towards my stepsons.
I'm sure there are many things that I don't know or understand about this situation but based on my take on what you have said so far, I still stand by my earlier comment and I recommend that you put your ego and (your tendency to be like your father) aside one more time. If it doesn't work out, at least you will know that you once again did the loving thing even if it isn't received well.
Your Mother is is facing death and her faith is probably a great comfort to her now . It's easy for her to be cold toward you from the other end of an email and though it probably wasn't a good idea to have sent her that Leah Remini information, I have a feeling that when face to face with you, your mother will once again behave like the true person she is inside and will at least momentarily put aside the Watchtower dogma that is clouding her true identity. Perhaps you could bring that family friend with you so that she will have to save face a little and behave decently.
The relationships I have with my wife's sons could have been much better, and I have readily admitted to her and a couple of other close friends that she married a broken man thanks to what this cult did to me.
Not to sound harsh but you say you have regrets regarding how things went in the past with your stepsons (we all have regrets like that). For better or worse, you only have one Mother and when she's actually gone, a bit of your own light will go out as well. In my mind, this is your chance to keep from possibly having another regret hanging over your head all because of your having once been associated with Jehovah's Witnesses. Don't let them rob you of this one last thing.