My father died about 5 years ago. For the last few years of his life (5, I think) he lived with his girlfriend, and their adult daughter lived with them. I live several states away from my hometown where my father lived, but we saw them at holidays and family functions, obviously, as they were seen as an extension of our family. The woman saw us as her step-children (her adult daughter even referred to my dad as her dad, and me as her step-sister, even though they weren't married. I didn't love it, but it was what it was). Now that my dad has passed, I make a point to have dinner with the woman and her daughter at least once a year (when we go "home" to visit family once in the summer). I am getting married next summer near my hometown, and I know she'd be a little hurt if I didn't invite her. But my guest list is very small.
Should I invite my dad's girlfriend and her daughter? Or is there a polite way to tell her they didn't make the cut?