I'll never give up on Dad?

my step mom has brain washed my dad for yrs. always saying her girls where perfect while my sis and I were full of evil, even after 20 yrs.of living out of there house my sis and I both have our own families houses cars etc etc. her girls 1 in prison and the other one on her way, and STILL it's never there fault. growing up I thought my dad was the greatest but to this day my stepmom does her best to keep him full of lies about me and my sis even though I can't remember the last time I talked to them I want my kids to know there grandpa but don't want the drama, and when I've tryed to call to talk to him she picks up the phone and will say he's not home when I have stopped by to see him she always makes sure to never leave the room. I even tryed sending a letter, but he never got it. How can I let him know, no matter what she has told him over the years, i still love him and miss him alot, and wish he could spend more time with me and the kids, I don't feel he cares anymore??